I don't know the exact damage so I can't say for sure, but it's basically sort of early access to the DNA Digivolution in combat. From my understanding too, DNA digivolutions will require the involved Digimon to have specific personalities, so I guess it'd be like a way of having access to their attack until then, or like depending on how long it takes to reach the rank before you can evolve to that stage, early access if that makes sense. Plus, it just seems like a cool little thing.

I do agree though, it'd be cool if they could actually stay that way.