On fish that are big enough to necessitate grabbing the gill plate, there is a considerable amount of room between where your hand hold is and where their lungs (gills) are.
I am not saying that every fish requires that you grab the gill plate, but there are some that this technique is designed for. There is really no safer way (for fish or fisherman) to handle a big musky. This gives the fisherman a safe way to control the fish, which actually protects it from injuring itself during the release. Big fish like that HATE to be in the boat and will usually go nuts on the floor.
Ideally, handling a fish as little as possible is the best policy. If you do handle a toothy critter for pics and getting the hook out, the gill plate grab is effective.
Wayne