Even omnipotent you gotta plan shit. Just can't be *blink* and everything is in place and works as should. Destroying is usually gonna be quicker just on the grounds it requires far less thought process.
I don't think the Bible paints him as omnipotent anyways. I mean he had a bet with the devil regarding a guy named job iirc. If God was omnipotent the devil was a fool to take the bet.