I've been stuck on TVtropes the past couple nights. One thing they bring up a lot for Twilight, is that no matter how powerful her magic gets, she still manages to screw things up, or that the big evil guys are more powerful than she is anyway. So, coming from a fantasy point of view, nothing will change. As far as day-to-day stuff, she can fly now. It was only a matter of time before she perfected that spell anyway, and she could already teleport.
What I want to know is, what kind of new powers will it grant her?
Well, get mad at the writers, who didn't get to the "history of the princesses" episode that was rumored and possibly true. And once again, that just throws the question around yet again, what about Cadence? She doesn't seem to have any royal duties, but her magic is pretty powerful.
Cadence brought up enough questions considering she's a relative of Celestia's, but not herself immortal and while her power is quite strong, she can't make the sun or the moon rise and Celestia can do both, though Luna got her old job back.