I'm a NYCOM student and I really don't know what is offered at other schools. I also just finished my first year, so I really don't know much about residencies, boards, etc. As far as the benefits go, the tuition is the concrete one, but the others are somewhat subjective.
For one, it gives you the opportunity to participate in the teaching process. It also gives you the opportunity to develop somewhat of an expertise in the particular field. It is certainly good fodder for recommendations in the future, providing you serve well. You have to weigh what your goals are and determine if these positions will help you reach those. It so, go for it; if not, forget it.