The only limiting action is doing math, for those that are freaky good like my wizard player this is OP, he did 14 tests in last nights game, took upto 1 min each and made it 13 out of 14 times. I allowed him to roll and math it out before his turn. Biggest effect I saw was casting quickened lvl 1's and 2's. Allowed a ton more versatility to a wizard. I honestly cant say they even remotely needed it. He is going to train back out of it.