Reply to Titles and Services Explained

Can some one tell me exactly how a booking agent works, and how are record labels and DJing firms supposed to benefit an individual?

I understand that a booking agent is supposed to get you gigs, but how, and what kind of compensation should they expect?
I understand that record labels release your music for you, but what else can they offer besides a bolstered paycheck and more fans?
I understand that a DJing firm unites local DJs under one name to horde business, but what else can they do?