One of the complications of putting on the musical, Grimhilda!, is how much use do we use mics? Some of the cast will be fine without them, but we have two kids in the show each night, and sometimes they have to talk over music playing in the orchestra pit, and, of course, they'll be singing with the orchestra. It seems logical to use mics for them. But what about other members of the cast? Mics are an expensive item in the budget (especially if there of the quality of primacoustic, for instance) and supplying them to everyone isn't going to be an option. Which means that the man controlling the mics is going to have his work cut out balancing miked voices with unmiked ones. It's going to be an interesting process.
When you're rehearsing a show there always seem to be some members of the cast who are comfortable with using a stage voice even when in a smaller rehearsal room, and some people who find the size of the space inhibiting. Once they're out in the theatre their voices bloom, and you can hear them easily wherever you are. But in the rehearsal space you sometimes despair of hearing them at all anywhere else.
And it's easy for inexperienced cast members to forget that they're going to have to throw their voices further than a couple of metres once they go on stage. I don't know why that should be, but it is the case. I prefer to be using a stage voice (somewhat modified to the surroundings) from early on in the rehearsal process. It makes the transition from rehearsal room to stage a much easier one.