as soon as overdubs are an option i try to have 1 session per song.
overdubs call for playlists pretty fast. (can we just quickly redo section C with the 1st violins only? o wait, let's use it as a double) an there goes your template...
add playlists and groups, occasionally add a few tracks and do that on a all-songs-in-one-session and desaster is near. if you add a track to a group that already had playlists, funky things can happen when changing playlist...
i recently got a session of a piano trio to mix that was build in this manner. 340 ***ing tracks, for a jazz TRIO!!!
with mutes, deactivated, cryptic tracks, takes, playlists allover the ***ing place. it took me 1 day and a few phone-calls and session-pics mailed accros the globe to get this sorted so that i eventually could START mixing.
It takes less than 1 minute or the time to properly tune a violin to do a SAVE AS, hit CMD SHIFT A, CMD SHIFT B and remove all markers and you are ready to go.