It seems like it gives you "respect" which is basically diplomatic relations. If you have a ton of it, you can *spend* it to open a jump gate. 500, the only time I was given the option so far, but it might vary.
It does seem like it would take a long time, though. I don't know if the rewards for higher-tier arena fights would be more worth it.
The fights themselves grant you Rez, but with diminishing returns for repeating a fight.
I have no idea if any of those benefits are compelling enough, but that's all I know of.