Different grips are used so that you learn to develop force from many different leverages. I've done a ton of different cycling methods for speed work like typical waving, 50, 55, and 60%, with pin presses, boards, floor press, chain, bands, and all kinds of other stuff. I feel at my most explosive when I stick with about 40% bar weight and change up the bar/chain/band combination every week. For example, week 1 would be something like a fat bar with mini bands for 12-15 sets of 3. Week 2 could be a bench log with chain for the same sets and reps. Week 3 a thick power bar off a 2-board with 55% bar weight.
You should never, ever be tired from normal speed strength work. If it is wearing you out, then you are either going too heavy or you have accommodated to the exercise. So, either way, you either need to back off or use a different variation or both.
Dynamic efforts arent just about speed. If you are doing westside like you are supposed too, there is very little volume control of the main lifts on max effort day. The strongest lifters arent stronger because they lift heavier weights in training, they are stronger because they can handle more volume without breaking down. Speed work, using the interval method, is the only way to monitor progress in terms of power, work, and time. Lifting and getting stronger are all factors in physics that have to be considered if you are serious about training. Power=Work/Time. The more work you do in the less time, the more powerful you become. You can't increase power on max effort day because the point is to rest long enough to move maximal weights.
Probably most important about the speed work is the benefits it has on soft/connective tissues. You learn how to store a stretch reflex longer. This becomces important when having to hold a long pause on the bench press and firing out of the hole in a heavy squat.
I dont know if I have been over thinking this shit or what but ever since I have taken the approach of looking at training based on physics and not just the weight I want to do, I have been getting strong as shit.