Hillel tells us that, when presenting a dance performance, the dancers should already be on stage when the audience arrives. He explains that only Hashem can interpret the world because only Hashem can see the entirety of the world to give it context and meaning. In a similar fashion, only the audience can interpret a work and give it meaning because only they have the outside perspective to do so. Since nobody in the world can hide from Hashem, neither should the dancer hide from the audience.
Ramban tells us that the dancers should be still on the stage and only begin the performance once the audience is seated since anything that they do before hand will be meaningless without an audience to observe it and interpret it. Rambam, on the other hand, tells us that the dancer should already be dancing when the audience enters. This is to signify that, just as the world is eternal and we cannot know everything that has lead up to any one moment, we must acknowledge that the audience can never have the full perspective over a work that Hashem has over the world: there will always be work that went into the work that the audience cannot grasp and so this limitation must be expressed to avoid the hubris of pretending to have the perspective of Hashem, even over a dance concert.
Rabbi Geiger tells us that the dancer must consider the social context in which they are performing when determining how — or even whether or not — to be on stage when the audience enters. It is more important, he argues, to look at each audience member’s personal experience of the work to determine how best to present it to them.
Buber tells us that the dancers should be directly interacting on a personal level with the audience as they enter. It is only in doing so that they can establish the I/You encounter necessary to have them fully engage with the work of art. The audience’s sense of being outside of the performance creates too much distance and, truly, it is the sublime melancholy of the audience’s lot to have to have an outside perspective and have to interpret the work instead of being drawn into it.
Common courtesy tells us that if having the performers on stage when the audience enters adds nothing meaningful to a performance then it is rude to both the venue and the audience to not open the doors and let them be seated half an hour before curtain. Seriously, folks: standing around in a lobby — if you’re lucky enough for the venue to have a real lobby and not a hallway or a sidewalk outside — is usually not the most comfortable way to wait for a show to begin. In some cases, having a performer on stage at the time that the audience enters can be poignant. Usually, though, it’s little more than a hackneyed and somewhat obnoxious gimmick and the aesthetic concept of the piece would be better served with a well choreographed entrance.
Note: I’m pretty sure that not a one of these great thinkers wrote anything remotely resembling what I said that they did. Still, give this technique a rest so that it can still be meaningful when it is appropriate to use it.