Nervous habit.Why soak them?
Just dry and hit 'em with cooking spray.Great idea, but unless you have stainless steel grates, that looks like a guaranteed way to make your grates rust years before they would if you did nothing but brush them off before and after each cook. Soaking cast iron grates would be a disaster. The chrome plated wire grates don't much like moisture, either. Building up layers of cooked on crud is the only thing keeping the chrome plated wire grates from rusting.
Why soak them?