Since the 7' banners are an advertisement for the theatre, we want to use photos from actual shows. We don't have a special photo-shoot just to get a shot for the banner, so what I shoot during the live dress rehearsals over the course of the year(s) is what we have to work with. Obviously, changing or augmenting the stage lighting is a no-go, as it can totally destroy the very essence of what you're trying to capture. Although some stage photographers will do posed (or semi-posed) photos of key moments, I dislike doing that. I find the actors have much better in-the-moment emotional responses during an unhindered performance than when doing a static pose, or even when repeating a portion of a scene for the umpteenth time. Especially when working with non-professional actors. I like the end results better, when shooting this way, and sometimes the most dramatic shots end up being from scenes (or portions of a scene) I would not necessarily have chosen for a posed photo.

It's much like wedding photography during the ceremony and reception -- what you get is what you get, and there are no do-overs. There's no interrupting the priest with an "I'm sorry, can you re-do the 'you may now kiss the bride' part?" I do, at least, get to shoot multiple dress rehearsals for a show.

edit -- tl;dr: my approach to stage photography is a photojournalism style