Rehearsing Mid-Season

I won't name show or anything else incriminating, but that's what we are about to do.
What is there general opinion on Hastily called Mid-Season Rehearsals?
When I say mid-season, I mean the show has already performed to live audiences (as opposed to dead ones ;-) and suddenly a rehearsal is called.
I personally do not like the idea. Fair enough if it a very long season, and I mean long. Fair enough if it had been planned earlier in the piece (like before the show goes up.)
But really, I don't how to feel about this one. I'm upset, that much I do know, but why?
Thoughts?
Jeff "Con-fused" Watkins