I'm curious. Does anyone do final mixes with hot soft synths? How does it work out?
I always bounce soft synths to tracks as soon as I can once I've gotten the sound design bit done. It gives me consistent levels to mix with and I can apply further effects processing and EQ to the audio. If I find something that doesn't sound right in the mix, it only takes a few seconds to go back, fix it and rebounce the track. Doing it this way also enforces the standard production workflow phases (composition, sound design, performance, mixing, mastering). Features like Freeze Synth have always seemed sort of redundant.
Are there any advantages to having live soft synths in the final mix?
 

Some bounce the softsynths because some synth sounds vary all the time, giving a different result every time you play back. So, to make sure the track is "stable", they bounce it down. Otherwise it's up to you which you want to do it, if your PC can handle the load.

I like to freeze my synths before I start mixing. One reason is it allows me to use FX without taxing the system too much. 

TomHelvey
I always bounce soft synths to tracks as soon as I can once I've gotten the sound design bit done. It gives me consistent levels to mix with and I can apply further effects processing and EQ to the audio. If I find something that doesn't sound right in the mix, it only takes a few seconds to go back, fix it and rebounce the track. Doing it this way also enforces the standard production workflow phases (composition, sound design, performance, mixing, mastering). Features like Freeze Synth have always seemed sort of redundant.
Are there any advantages to having live soft synths in the final mix?

AFAIC you've defined "best practices" for dealing with mixing soft synths. It's convenient that Sonar does let you archive the tracks so if you change your mind later, you're covered.
 
I do leave them "live" as part of the mix if I'm going to alter parameters while mixing, or keep tweaking to reflect changes in the mix. Even then, they usually end up getting rendered at some point.

I freeze most but bounce some because I find that freezing does not give reliable results for some things.
 
I freeze the ones that stream from disk or use a lot of CPU—and that I know will freeze reliably.

I like to leave them live if I'm doing a "demo mix" to throw in my car, try on various sound systems, etc. Once I commit, I like to "save as" project name audtrx mxdwn, (or similar) bounce and then kill the softsynths and midi tracks altogether. (they're still there in the original file). Then I know I have the most resources available for mixing plugs, etc. Plus it leaves things lean and clean if I decide to control any of the mix process with automation, etc. I hate having to hide/unhide and otherwise manage more tracks than I need to.

Freezing is very useful if for example you have pads with long sustained notes and you frequently need to start playback in the middle of these notes. Without freezing, the part will be silent until the next notes kick in. When frozen, you can start playback from wherever you like and the notes will always sound as they're supposed to at that point.

I never even think of freezing. I always thought that was only to conserve CPU loading and was from forgotten days of wimpy computers. So I just mix live. Never had anything sound any different that it does in Sonar. 
Like Greg I like to continue tweeking.
And you can add audio effect to the Soft synth audio output tracks. 

One thing about freezing/bouncing/recording: you always have the wav if the VI stops working.  I have had Vienna suddenly stop because of an eLicense issue before.  One time when I upgraded the Electri6ity library, the application quit working.  Sometimes after systems upgrades, the DLLs for other things have gotten messed up.

That is a good point. It's sort of the reverse of how I always back up CWP files as a MID. file too so that down the road at least that part of the song might still open on some sort of computer of the future. 
Saving all midi as audio for future proofing is a good idea. Thanks Konrad for that insight.