Its a game where gladiators compete, extra fights are a bonus. If your glad is good enough, the challenge will only push them up, (without you having to pay for a fight yourself) like with Ty Rex. I wish more people would actually do it (although I am certainly not going to keep doing it to the extent that I am, that was just a one time thing) as it would mean more money for the developers, and more accurate ranks (and perhaps Conquests would have been done by now).