Good: Reps, try tweaking some things with no real repercussions, different coaching perspectives. Draft implications in some leagues.
Bad: Very few of the kids actually want to be there. Unless you're in the Cape or a premier league, many are just doing it because their coaches told them to. They would rather be at the lake, the beach, or mostly just sleeping in and playing video games/catching up with home friends. Sometimes you will also be dealing with an inferior coach/staff that are also trying to make a name for themselves.