They're just filler mostly. But a lot of teams like to play the little schools in their region that they may have a small rivalry with, or teams that they feel might prep them well for say a first round NCAA game. Like Duke tonight, Davidson was an old Southern Conference rival, and they are in NC as well, plus they're the kind of team Duke would face in the early rounds of the NCAAs, so it's good preparation. Plus the little schools sometimes get paid to travel to the big team's court to play. It helps the little guy too because they get to gauge themselves against a premier team, which will help them in their conference, maybe provide some publicity if they're on ESPN, and should they pull off the upset, it'll help them a lot in their bid for the NCAAs should they have a great season but somehow now with their conference tourney.