I've been in this situation several times before--every time was at a summer stock theatre, though, which always seems to be a bit chaotic.
During rehearsal for the show, the stage manager took complete charge of everything in rehearsal, and I worked on building the show--sets/costumes/etc.
Before tech, the stage manager and I had several meetings where we went over the show--sort of a "heads up" to the big elements that I needed to be aware of. Basically, once added at tech, I become much more "run crew" and "scene change" leader, rather than ASM. I was rarely on com, often running around moving scenery and trying to keep backstage running as smooth as possible. Since it was summer stock, most of the actors were taking on the additional tasks of moving scenery, so I was responsible for making sure they all remembered their cues and their responsibilities--as well as my own.
It usually all worked very well and I didn't feel that I suffered because I wasn't in rehearsal the entire time, although there was a steep learning curve the first day of tech.
