Students learn best when they are engaged and happy. I have found in math class that one of the best ways to accomplish this is to incorporate games into our regular math routine. A lot of good things happen when students are placed in a game situation. Suddenly that math concept we have been learning is now being put into practice. Students who wouldn't normally ask questions during class feel much more comfortable calling me over in their small groups to ask for clarification and even help. And students hold each other accountable, making sure all players are performing calculations and applying concepts correctly. I see students teaching other students how to do something, knowing that teaching someone else is one of the best ways to learn and to remember how to do something.
The competition also adds an element of interest to students. I've read countless articles declaring that there is no place for that in math class, and that girls, in particular, suffer under a competitive situation. Perhaps competition that is "mad math minute" style is detrimental, but I see only positive effects from this style of friendly competition. Also, many of the games we play rely much more on chance rather than how quickly students perform, and I think that is key. Under these conditions, girls love the competition as much as boys do, and everyone benefits.