I also do that sharke. Especially if some of the other synth parts are monophonic in nature. (lead lines, bass lines, sequenced riffs) Then you can treat them as a point source mono sound that you can pan and effect. Adding early reflections only can really enhance a mono sound and not make it too wet.
 
Here is a way I found you can combine say three stereo synths. If you pan them all hard L and hard R then all three stereo images are going to land on each other. One approach is to pan the first stereo sound hard L and to say 10'Clock. Then the second stereo sound from 10'Clock to 2'Clock. The third stereo sound can occupy 2'Clock to hard R. This helps to separate three big stereo patches. You can turn them down now and still hear them.
 
Channel Tools is great for narrowing an image and it still can sound great. You can get inside the effects sections of many synths too. (real and imaginary) I know the more time I spend in there tweaking about the better you can adjust the effects over any given patch. They do tend to over do it sometimes and you can easily reduce reverbs, relax some chorus and ensemble effects, slow them down make then less deep, back off LFO's etc. In the Kurzweil you can move the panning of anything more inward and make it more mono. (not completely) Get it more right there before it leaves the instrument helps a lot.

Maybe I am reinterpreting what the OP's friends might have meant, or mis-heard.  I have been through several discussions about "checking" mixes in mono.  Many accomplished engineers think that is a vital step in mixing.  To sum all tracks and busses to mono, and listen for phase problems.  If a mix can achieve a sense of depth in this circumstance, it will inevitably improve the overall sound in stereo.  
 
I never got into this because of the nature of my recordings.  (mostly acoustic instruments using non-mono-compatible stereo techniques)
 
Personally, I will use stereo tracks only if the microphones themselves require a hard left and right panning to achieve the proper stereo signal.  Most stereo techniques from XY, ORTF, NOS, Blumlein, AB etc. fall into this category.  Even MS codecs usually require a stereo track.  Using spot microphones for certain instruments (such as a left spot and right spot for a choir) will be placed on two mono tracks that I can easily pan into the main stereo image.  

I think Daniel that you may be talking about something else again there but I personally think it is pretty important. I have got a single point source mono speaker in front of me that is always being fed a L+R signal. (I also roll off everything below about 120 Hz because there is no need for it. It stops the speaker farting around at high volumes and the bass end will still tell you a lot) This speaker is fed from separate amp by its own control. It is simple matter to turn one (main) set of speakers down and this mono speaker up. I spend quite a lot time on it during a mix. It is so honest especially at lowish volumes as to how well everything is balanced. It is ideal for setting vocal levels into music levels. It is not pounding you or your neighbours for hours either.
 
It shows off if a very wide synth sound collapses not well into mono. Sometimes the whole sound of a patch can change eg a severe mid range dip when some sounds are summed to mono. By getting this sounding good in mono ie back to no noticeable change in synth patch, it will sound killer in stereo too. You are pleasing two requirements compared to just one.
 
You can keep an eye out for things you know are quite wide in stereo eg some stereo rhythm guitar tracks that have been heavily effected. Is the tone still stable and can you still hear that clearly now in mono. The mono speaker can do all this. I also prefer one speaker compared to a pair of small speakers in mono. It is not quite the same thing. I would be a bit lost without the mono speaker.
 
Of course your mains will reveal lots like bass end, reverbs, and just how bloody great your track sounds up super loud after you have been so well restrained listening to it down low in front of a small mono speaker for so long!
 
 
 

I read on the net somewhere that recording tracks in mono is better because it's easier to edit them and I agree. Just my 2 cents!

I think it depends on what you are recording. If it is a signal that won't benefit from being recorded in stereo then yes you are right. 
 
The correct thing to do if you have got a nice wide stereo signal that can be simply placed on an interleaved track is to track it in stereo. It is easy to convert to mono later if needed. I find editing is no different with stereo or mono files. In fact I often forget which tracks are in stereo. 
 
There are so many places where stereo signals are present and in many cases it is overlooked and recorded in mono instead doing it an injustice. Guitar effects processors, guitar amps (Roland stereo chorus) nearly every hardware synth after a certain year, any nice stereo micing technique. 
 
Using two mono tracks to represent stereo is also OK and useful but the two halves can easily be put out of sync!

mono sources should be recorded in mono.
 
(bone simple, to capture and to mix)
 
stereo sources are invented by use of microphones, typically.
 
(if you have a wonderful sounding space, recording with stereo pairs is the best way to place your capture in 3-d mode,  you 'invent' the stereo source in a way your ears hear naturally, in human stereo, which is really 3 d)

 
electronic stereo signals, should be recorded in stereo.
 
(they were created to already be in stereo, mess with that and you've gone off on your own)

I personally love mixing in mono and checking things in stereo

sharke
I don't know a lot about this but I have found in my experience that if I have too many stereo synth sounds then my mix gets cluttered and unfocused pretty quickly. So I try to limit my stereo synths to the one sound (usually a pad) that has the best stereo effect, and add the others as mono instruments. For example, right now I'm playing with a resochord instrument in Reaktor that takes a sound source (in this case drums) and uses it to trigger 6 "strings" that resonate according to an input of MIDI notes. You can pan each string anywhere you like and it really is the most wonderful sounding effect. So that's my stereo synth, and the others I'm keeping in mono. If I introduce other stereo synth sounds, it kind of detracts from the effect of the resochord.

Yep.  This is an unavoidable outcome of far too many (IMO) synth presets being drowned in reverb and overloaded with delays in order to sound good when demoing them solo.  If you discard those cosmetics, the preset may be perfectly suitable for being treated like a mono instrument.  Which is not to say that spacey pads and the like should be reduced to mono.  It all comes down to the preset and the nature of in-synth effects in the preset.

Beathaven
I recently had a discussion with a few friends (who have varying degrees of understanding of mixing and mastering - amateurs all) re. mixing and mastering. One of my friends said that he had read somewhere that to achieve the best mix prior to mastering was to record all tracks - whether instruments or soft synths - in MONO mode and then using pans to seat the tracks in the image - whatever that means. Is recording tracks in MONO really the best way to go when mixing?

 
Hi,
I don't care about what's best or not, but I remembered something cool. I don't know if you tried this already...
Not quite sure on how to do this in Sonar (I guess is by using the send and send pan knobs) but an old trick is to create stereo images from a mono source by using a delay. 
Setup a delay for the source on a separate track, zero the feedback and adjust the time in just a few miliseconds (less than 30, for instance). Pan the original and the delayed track opposite sides. That will create your stereo. The cool thing is play with the delay time and pan knobs. I learned that as a trick for HHs in house music and I always use across different tracks.
  

This ^^^ sounds like the Haas effect