You might as well not compress on the way in anyway. If you do, and you don't like what you've done, you can't undo it. Might aswell compress afterwards. It's not like you don't have a buttload of headroom to play with anyway with digital.
That said, sometimes vocals could be helped with light compression on the way in if you're expecting a reasonable dynamic performance.
My music being somewhat instrumental at this point, I think the only thing I ever compress on the way in is bass guitar, and that's only because my pre has a comp bult in, and even then that bass track is put quite low in the mix next to a track I didn't compress on the way in. And that's if I don't just throw it away, which I often do.