Ok, I completely get it now. Yes, Bubbles by themselves are really bad. However, Freeze gems are great, especially if you get more of them. And somehow I hadn't actually noticed that when Bubbles Freeze, they *become* P-Attack gems (since that's the gem that gets enchanted with Freeze), regardless of what gem type they were before. So it not only gives you more Freeze gems, but more P-Attack gems too.