Each person will grip with slightly different pressure based upon their own unique muscular development. When I say light I don't necessarily mean no grip at all. The important fundamental, I believe, is an actively relaxed grip. Of course the musculature of the hand, wrist, arm, shoulder and core and the rest of the body for that matter are all going to be active, but they should not be over active which is to say tense. It should feel relaxed and smooth while still getting the job done. It takes a lot of practice to get a relaxed yet powerful stroke.
The tendency when one wants to hit with power is to want to bear down with the hands. It is a natural reaction. The brain is used to the idea that a firmer grip means more control, especially in pressure situations. Over active muscles, especially if their level of involvement changes throughout the delivery of the cue results in more often than not and inaccurate contact point on the cue ball. To make that worse the tightened grip can lead to an unnatural follow through where the cue is manipulated in a motion that is less than ideal in delivering the cue ball forward along the intended line of travel, and also can be random in nature which makes it hard to repeat.
I have seen many really good players with idiosyncratic deliveries. The problem with a lot of these deliveries is they tend to be dependent upon timing. When the timing is on it can be a thing of beauty, think Busty. When the timing is off it can seem like a train wreck. I used to hit with a much more idiosyncratic stroke, figuring that it has been working thus far and it can get the job done fantastically at times, but I have been much more consistent since I have worked out a lot of the timing elements of my stroke. My delivery is far more consistent and repeatable now than it has ever been. Light grip, compact efficient cuing and straight smooth follow through.