Sitting through an audition provides an opportunity for some fascinating people watching.
There are those people who try out because being onstage would stroke their ego into gargantuate proportions. It's not because they are interested in acting, or cast chemistry, or evolution of character. They come for the audience greetings at the end of the show; the compliments, the praise, the gushing and hugging and handshaking. These are the people who refuse ensemble parts because if they don't have the leading role, they wont be involved at all.
And there are those people who can't stay away because they simply love everything about the theatre. Yes, they come hoping for a certain role. But in the end they'd rather be involved on any level in the show, because being around actors and scripts and costumes and lighting is so intoxicating, they can't live without it.
O, the plastics and geeks of theatre.