DPS meters aren't needed but I do miss one in this game.
I'd like to see how well I'm doing in comparing to the others, what skill do they use etc., actually I learned A LOT in WoW thanks to Recount I could inspect people cycle and that made me want to try other classes by learning more about them this way.
Also, you can help people by telling them what they are doing wrong; it's a great way to learn.

And the final point is.. It makes the dungeon a bit less boring, I personally can't chain dungeons all day without something like that to watch to "entertain" me.