Small fish will move or turn in the water when the hook is set. Bigger fish however do not move as much on the initial hook set due to their heavier weight in the water. If, when the hook is set in a big fish, the line, the rod or the fish do not give much then there is only one other thing that can - the flesh and bone of the fish. I used to set the hook about as hard as I could. I noticed however that I lost a number of fish on a jig even when the jig was deep in the mouth of the bass.
Hooks work best when they puncture a small hole and allow the barb to hold.
The down or outward pressure the weedguard creates is minimal and depends on the stiffness of the weed guard itself. However, it does not take much pressure to cause a problem. If a big hole or slot is torn in the mouth of a fish and the bait slips back at all, the weedguard, which is continually pushing against the mouth of the fish, helps pop the hook right out of flesh or bone and the fish spits the jig. It goes without saying that if a bass takes a bait and is hooked in the side of the mouth then the bait can be torn right from the mouth with relatively little force. Again, a small fish may move or be pulled in the water enough to absorb the shock of the hook set, however, big fish are much harder to turn.