i think folks should never go into a studio without having their act together.
booking studio time, is not the time to experiment or 'wing it'.
you should be able to nail your part in at least 3 passes, no more.
working on your own stuff, that's totally different!
work for a year on one bass part, who cares!
but, i find that WRITING MUSIC, even at the DAW, is a different process than TRACKING A SONG.
one happens first, then the other.
if you are well rehearsed, and do not have to struggle with the mechanics of pulling off what you want to do,
this is what allows you to be free and creative, and get the 'feel'.
ideally, for myself, once i have finished writing a part, and know it totally,
i walk away from it for a while...
come back, warm up, and try to get the entire thing from beginning to end in one pass.
that always sounds and feels better than hacking something to death in bits and starts.