So we all know that a pet can only manifest five of its talents, getting a new one every time it progresses in age. So why is there an ultra rank? By the time your pet reaches Ultra, its stats will be maxed out and the final talent is unlocked at Mega, so what's the point? What do you gain from training a pet to ultra? Does it get another jewel slot at that point?
I wish it would get an extra jewel slot. Wouldn't that be nice?
But no, sadly, the only reason to train to Ultra level is if you already have an Ultra gem that you'd like to socket.
Alia Misthaven
PS: in the interest of being completely honest, training to Ultra will net you an Ultra-level gem, but it's always been a stat-boosting gem in my experience. The gem you get for training is almost never worth the effort involved. So yeah, only go that far if you've already got a great gem that you'd like to use.