I'm going to a conference next month. This conference is one of my favorites, but I haven't been to it in 2 years. It is always a great group of people. Plus, this year it is in a fabulous, exotic location.
This year, I am competing in the best student talk competition. I've done this sort of thing before and have enjoyed it. One side effect is that the talk itself is better. Being comfortable giving talks is an asset but that also means that sometimes I don't practice or prepare as much as I should. When I know that there is more on the line- being judged, being in a special session, money (!)- I prepare and practice a lot more. Depending on the meeting, participating in these competitions can also give you leverage for networking. If there are limited numbers of students, either through an application process or just because few bother to apply, there is a greater chance someone important might take notice of your name, see your talk or be more receptive to your intellectual advances later.
My ex-advisor thinks I am all cutthroat about winning because I've done these competitions. Maybe he doesn't realize that I put my participation in them on my cv! I admit, there were a couple conferences where I was all about winning, but I was required to go to these and really just wanted some prize money to offset the cost of travel. This upcoming one is the last one I will do as a student and at this point in time, I am really in it for the game instead of the prize. That doesn't mean I'm not going to work my ass off to give a good talk. But I will be happy knowing that I've done my best and will value the indirect benefits (like the networking) and experiance more than a prize.