The point is that, after it's been out a turn, you can drop a weak evolving basic onto it and immediately evolve it. You can also use it in toolbox decks. If I put 3 prism on a Ditto, you have absolutely no idea what I could hit you with to respond to a KO. It could be a Terrakion, a Darkrai, or whatever the situation calls for. It's a very hard card to use, and it's very skill based, but it can be quite useful in the right deck.