The ability to award extra rep or a badge to users who make some kind of great contribution, kind of like the Wikipedia Barnstar idea.
Advantage (at least of rep) is that it is completely scalable (e.g. 200 rep awards for 20K users, 300 rep for 30K etc.).
Disadvantage because it is subjective some people who don't get these awards may ask, "Hey, what about me? That's not fair" and it may create a bad atmosphere.