There are two specific things that I get out of PL games (aside from the usual fun):
1. It's a chance to test out my lineups in games that don't really count and don't effect game shape/training, to see if certain combinations work well together and in certain offense/defense situations, and really get to know my roster strengths and weaknesses.
2. It's a chance to play against some teams that I know are way out of my league, to see just how far I have to go to develop my team into a team that can success in higher divisions, and to see what the better teams are like and how they play games.
In short, PL leagues are maybe the one Supporter feature that, while not giving us a direct tactical advantage, does give us a small edge in helping us get to know the game and our teams a little better.
Don't ask what sort of Chunks they are, you probably don't want to know. Blowing Chunks since Season 4!