If it's anything that bleeds into the start of what counts, either in effects or dry, I tidy things up during the mix. Otherwise I trim up the ends up when I take the mixdown track and set it up for the final CD tracks.
Indeed, Karl, I would do this myself, it's just in the song body or periods of silence I would do this as per Steves reply
Chances are that the average listener wouldn't hear it, unless it was at the start or end of the whole track. But that said, it's sloppy practice not to trim the detritus, and with 'exposed' acoustic material it is usually audible, and quite unwelcome
If you set up a key combo (mine's CTRL-SHIFT-M), just select everything before the entrance (and after the exit, or whatever you want to cut in between) and hit the combo
Ahh! i get it know, like shortcut keys(wasn't sure what combo meant) and mute the selected. I was fading(envelope) this 'cos I didn't want abrupt intro and outro and sometimes I liked the suck of breath sounding out in the song.

Manly sounding

With guitar etc I wouldn't dream of leaving anything at all 'cos who wants to hear you turning up the volume before playing?
Mark