Real world example:
 
I have spent the last year writing/recording an album of original material, but have been struggling to find the right singer.
 
I have recorded all the instrument parts, with me singing guide vocal parts.
 
When (if!) I find the right singer, I will have to mix the instrument parts around his/her voice.  Being able to change the sounds/voicing to suit the timbre of their voice will be a godsend.

I always leave myself the ability to unfreeze and modify midi data, as well.
 
I have 32 GB of memory, so I never really run into problems, 
 
Bob Bone
 

There are those amazing planners who can see the end result even before they start tracking. They are usually famous as a result.
It probably helps if it's not your stuff and the tracks come more or less complete along with a demo of intent.
I suspect most of us who do originals, do a lot of improvising along the way and we approach from any angle. 
For me, often songs start from scratch tracks to be added to and thrown away and they can take shape or change from any point in the process.
Often the hardest part is knowing when the damn thing's done.
 

Sir Paul McCartney used to hang on to song snippets and glue them together - such as Band On the Run. 
 
The piano ending to Layla was written and recorded and stuck on the end after the first part was done.
 
The best advice I can offer is to follow your own light, and try not to run out of batteries.
 
Bob Bone

No need. Think flexibility is the key to producing the best result.

Bibs

aglewis723
 
Even that stuff technically "should" be done in the tracking phase... it's still musical edits, no?  I could be wrong, or maybe there is no stinkin' rules, its music for God's sake :)

You are indeed too focused on rules. Forget about them. Do whatever is necessary to get a good song. 
 
Obviously it also depends on how you record your music. When you are recording a band then you might record everything live in one go: then you will indeed mix when all recording is done. But even then you may discover something is missing or wrong during mixing and you may have to record another part anyway. I myself make music on my own so I record one track after another: in order to play and arrange and record a new track, the existing tracks HAVE to be mixed to a certain extent otherwise it may sometimes be impossible to do it well. So it all depends on the workflow for a specific project. But even then: forget about the rules: there aren't any (in this regard).

I used to bounce but now I click the Include Live Audio in the export box.
 
I tend to freeze the CPU and memory killers like Hollywood Strings, Dimension Strings (if I have loaded a lot of articulations), but let other things like drums, bass, RealGuitar, etc. play live.
 
I often record external synths before mixing because I fear something will break.

I'm with "...Wicked",  everything is audio at time of mix.  You have total control with EQing, Compressing, etc. that way.  And if you need to change something with a softsynth, you always keep the frozen synth track (or midi track) in an archive folder.  ; )

But the point is - a "frozen track" IS audio. But it also has the HUGE advantage of one being able to easily edit a change or a make a  fix, change key etc etc, without the need to punch in record or go into arcane audio editing tools et al, which don't often work all that well and you are forced to go through another time-consuming and frustrating re-recording session, which takes even more away from the inspiration one started with
 
Just one tip though, by default Sonar disables the efx bin when a track is frozen. You do need to  re-enable it by right clicking on the bin

californiamusic
I'm with "...Wicked",  everything is audio at time of mix.  You have total control with EQing, Compressing, etc. that way.  And if you need to change something with a softsynth, you always keep the frozen synth track (or midi track) in an archive folder.  ; )

FWIW-this is exactly how I do it, audio only for mixing.