It really is one of my favorite songs in the show. But not only is it good in and of itself, it has many great meanings behind it, IMO. First great thing was Twilight being able to have so much support from the other Princess;. Then it helping her with what she was struggling with being a Princess but not knowing her role. But even beyond that I think in a way it can also apply to others. While chances are I very much doubt any of us are struggling being new Princes/Princesses or anything of that caliber, I think most of us do struggle with finding out what our place and role is.
When I listen to the song it has so much meaning. I think one part that is especially poignant is when Celestia says:
"Your destiny's uncertain, and that's sometimes hard to take. But it will become much clearer, with every new choice you make".
I have certainly felt the same in my life. Never knowing what I am supposed to do, where I should be, what my life is supposed to be. But I have made lots of choices, and while good and bad it has helped me to realize more what I am, and just what I should do.
I just find it a good song for so many different reasons, not least of which is the message.