As always, it depends.  Upon the song, the gutiars, what part they play in the entire arrangement.
 
If you wide pan one of the interesting things to do is bring the lead guitar (if it is playing along to the rhythm from its pan setting all the way to the center.  It brings the focus to it (esp. in conjunction w/ vol) and mimics the visual of a lead guitarist stepping center stage, tho sonically he most likely isn't dragging his marshall stack to the center w/ him.
 
@

I use as many as six guitar tracks for a rhythm part. Mainly, I use two cabinets, each with it's own mic in separate rooms. I will have the guitarist record a Left, Right, and Center (usually with a different guitar). I'll pan the Left and Right 100%, then bring up the center guitar just enough to fill in the gap. During mastering, using M+S leveling, I will typically bring up the Side channel slightly to increase the image width even more. However, keeping in mind the center guitar is still there to help fill in the middle hole.
 
It's three different guitar tracks, two mics on each.
 
If you are dealing with a single guitar, or you've got a lot of cymbals or other keyboards, vocals, or sounds going on that need some sound-stage, I say fill the sides up with guitars.

With tunes that have some complex technique involved, for acoustics I will record with one mic through one pre and a different mic through a different pre each with slightly different settings. Then I will nudge one slightly and pan to fit the balance of the song. I find the mic/pre coloration is helpful for getting a slightly different tone which helps with separating the sound as two different takes.
 
Years ago I would have double tracked possibly doing the same mic/pre technique. Sadly I'm finding the years adding up...
 
Regards,

.... if you use the  "CLONE AND NUDGE" you better be checking your mixes in MONO due to the very real possibility of comb filtering which can and will happen and will totally destroy a mix that is acceptable in stereo.
 
Nothing is free. And that particular shortcut is fraught with perils. Take the time to record a new track... don't clone for this purpose.
 
You have been warned.

Can't you just invert the phase of one of the tracks to deal with comb filtering?

Interesting thread, lots of interesting replies
 
My take on this is when I mix and maybe pan the rhythm and lead guitar tracks fairly extreme using either speakers, but if I listen to that mix later using cans, I tend to lighten off on the panning to some extent

Beepster
Can't you just invert the phase of one of the tracks to deal with comb filtering?

 
I would think not.
 
I suspect it would make the issue much worse. If you take 2 tracks (CLONED) and invert the phase on the second one and do not nudge them, the perfect alignment will result in total silence as one cancels the other. Now.... simply nudge one of them and you probably will have sound to one degree or another, really bad sound....essentially, the exact opposite of comb filtering.  Comb filtering is the result of certain frequencies that are out of phase to the point where they are canceling to one degree or another, the other while most of the frequencies are not canceled but are still, none the less affected to some degree. The higher frequencies are the most noticeably affected by this cancellation effect.
 
I have not looked in to this topic in great depth, BUT.... anytime you take 2 frequencies and combine them you automatically create new frequencies. You get beat and harmonic frequencies below, but mostly above the original frequency, as a result of the two you are combining. Take a guitar string.... tune the string to a note, then tune another string to that same note. As the two approach the same frequency, the two notes start to interact and a beat frequency is produced. We hear this as a pulsing sound that slows as the 2 frequencies become the same. So throw that into the mix of a song, because that is what is happening constantly in the 2 cloned tracks as the frequencies change..... and you get comb filtering of the frequencies.
 
I'm sure the math on this is absolutely fascinating.
 
By recording two unique takes of say an acoustic guitar track, the chance that anything will be exactly the same, even with the same notes and chord patterns being played, is fairly remote. Not impossible, just not as likely. It's still a good idea to check all mixes in mono for such issues.
 
My first paragraph is based on my understanding of phases, nudging, and frequencies. It's an easy concept to test. Simply clone an audio track but don't nudge it... reverse the phase on one.... play it... you should have no sound..... then nudge one of them a few ticks and play it again. See what comes out of the speakers. I don't think you will be getting a full spectrum sound.... next time I'm in the studio I will do this myself just to check it.
 
just for grins, I looked at a few things.... http://en.wikipedia.org/wiki/Destructive_interference#Constructive_and_destructive_interference  this may or may not help to explain the comb filtering and why it occurs. In audio we call it by that name, but it exists in any thing that emits waves of any kind. we are simply operating on the very low end of the spectrum.... and check out the math on that page.... wow....!

Well either way if something funky is going on I'd like to think I'd hear it. Would be kind of wasting my time learning production if that weren't the case. After my last comment I went to youtube and watched some examples showing the effects of comb filtering. I've only ever looked at the Haas effect for guitars from a theoretical standpoint but now I'm recalling that the stuff I've seen about it  mostly dealt with doubled (not cloned) guitar tracks. I was getting a little mixed up I guess. I'll be experimenting more with all these types of ideas in the near future as I start actually putting some of these fancy doodads I bought to use. Cheers.

There is a short demo and discussion of Haas effect http://www.fabfilter.com/video @ 5:40 in the FabFilter Timeless 2 - Tips & Tricks part 2 video including how to mitigate comb filter (i.e. turn down the delayed channel). While all the videos feature their Fab effects, the videos are useful technique tutorials.

Beep - the 'flanger' effect is what it sounds like. That is the sound of comb filtering. Only difference is its moving in real time. A flange is just a clone with a very short delay, but that delay is cycled at a set rate and over set constraints. If you pause it at one spot (and you'll get varying degrees of thinness in sound), that's one of the sounds you might hear.

The inverting polarity trick as mention, will sum to zero as long as they are panned equally and opposite (eg 100:100 or 80:80). If different (80:50) then a little bit of the original sound will remain. There is really only one time you can use this effect I believe - as a little effect that's not important over all. You might have a little noise or something that sounds interesting out way out, but it doesn't matter that its lost when summed to mono because its simply an unimportant, interesting little effect.