LogFAQs > #949559631

Iirc coliseum grinding is really good but also a little game breaking. You can get some ultimate equipment early. It takes some specific strategies to beat certain enemies though.

I think its main point is getting the dragoon items. Edgar and Mog become pretty crappy in WoR, and the way you keep them going is either teach them magic (which is kind of weak) or give them a lance and dragoon boots/ring (don't remember if those were the item names) to turn them into jumping single target monsters. One of the items is in the coliseum, the other I think is easier to find.