I'm just going to take what
OhFancy wrote and give a little bit more details.
You get 4 votes, which is 3 more than regular players. All for that one map that you reeeally want to win
![Smile :) :)](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
You can join full lobbies, even if it's full of iron and gold donors.
You can ./disguise or ./d and ./undisguise, to randomize your name. It usually has 2 random words, and 3 random numbers at the end I think, and will either give you an iron donor rank or a normal player rank.
It lasts forever, or until MCSG shuts down.
Bragging rights!
It helps MCGamer keep running, and shows that you were willing to support it rather than those 5 random survival servers you've started playing on.