LGBT: Why do we need labels?

Even those people that don't like to be labeled, are constantly trying to put people into specific catagories. Gay, lesbian, black, atheist, tall, skinny, bi, white, squat, homely, christian, smart, weird, dorky, the list just goes on and on. I myself am guilty of it. Why do we constantly do this? Why do we separate ourselves because of gender or race or sexual orientation or grades or hobbies, aren't we all human?