Or was going to break himself or the bike. Which could happen, I suppose. I could also happen while sitting down, so, meh.

As for advantages inherent in riding standing up, um, your butt doesn't get as sweaty. And if you're cranking hard all the time then you could be pushing your leg muscles into an anaerobic state, which will help build strength and muscle mass, as opposed to endurance. The biggest advantage is that you enjoy how you ride; nothing else really matters.