Music has a lot to do with moving the crowd. I don't care who it is. It could be Mr. Olympia, but if he is using boring posing music, the audience is not going to be near as excited.
Your posing music should be a reflection of you, or at least make you feel comfortable and confident on stage. Furthermore, you should choose something powerful that will really get everyone's attention.
Your posing music has to be EXACTLY 60 seconds for most state and regional shows and 90 seconds for national shows. Most professional shows don't really matter. It could be anywhere from 2 minutes up to 5 minutes. But who wants to pose for that long anyway? Right?
Some great ideas for bodybuilding competition music are: terminator 2 theme, conan theme, superman theme, firestarter, voodo people, my way, are you ready, hell's bells, can't touch this, etc.