Everything you see on stage during a performance needs to be planned and well thought out. It definitely goes for the performances from the actors, but it also goes towards the other, less obvious elements of a show. It's the Production Manager's, Stage Manager's and in our case, the Writer's job too, to make sure that everything is set for the performers and the director so everything runs smoothly.
For every hour of rehearsals, we only have a few minutes of performance. It's up to the Director and the Writer to make sure that the cast knows what they're doing, and that everyone is working towards the same goal.