Advantages: well, no worries about unwanted pregnancy. you can participate in things like pride parades...and you can hook up easily in public washrooms! Haha. I guess it also sort of encourages you to be really accepting to everyone, and less judgmental.
Disadvantages: Social stigma, obviously, lack of rights in some countries, you can't procreate on your own. Also, there are quite a few more straight people in the world than LGBT, so it's harder to find a partner.
But honestly, if you're gay, you're gay and there's no pros/cons list needed. You can't make that decision.