It depends on the rep. You're playing Don Juan? No problem, know it like the back of my hand, just tell me when to show up and I'll watch for the tempo changes in all the usual places.
We're doing Boheme? No way I'm doing that without a dress rehearsal. Every opera singer screws things up in their own special way and I need to know what to expect.
We're doing anything by Stravinsky? I'll take every rehearsal I can get.