It means "it's great to be good-looking." In other words, good-looking people get all the benefits in the world. People are nicer to you when you're good-looking. When you're good-looking, you get a better job, a higher pay, an equally attractive spouse, etc., etc. An extended version of the saying is "人帥真好，人醜吃屎”, which means "it's great to be good-lucking, and if you're ugly, you eat shit" (I know, it's vulgar, but that's the expression).