I use separte drives for each. One for recording, one for playback and another for OS.

The purpose of separating recording from playback is diskthrash from the drive trying to keep up with reading chunks all over the drive (due to editing and mixing) and then trying to keep up with writing the streaming input at the same time. Too much jumping around.

So to avoid this it is often better to have OS and playback on one drive (where you save the song is the playback drive). And then use another for recording to, especially if you record a lot of tracks. This is if you only have two drives available.
Once you 'keep take' I think the audio gets moved to the project drive (playback; where you stored it) but that may not happen until the next save is envoked, not sure .. and this may be part of why RB is able to ask "recover data from last session"? as an option after a crash. Maybe it doesn't move those temp audio files (recorded tracks) from the orecording drive until it closes..

I do not work here, but the benefits are still awesome
Make your sound your own!