Mechanical reason why grip change is important

Recently I was very surprised to here someone had been told that switching grips between hitting forehand and backhand was a bad idea. Here is the mechanical reasoning behind why switching grips is vital to a strong forehand and backhand.

Switching grips prevents slicing

If your ideal contact point to hit the ball was dead center in the middle of your body, then there would be no need to switch...but it's not. The ideal contact point to hit the ball is just inside your front foot. At this point in the swing your arrm--and wrist--starts angling upwards slightly, causing you to slice or cut the ball slightly unless you change grips. If you don't change grips and roll your wrist to correct for the slice, then you have significantly weakened your wrist strength when making contact.

Two grips, same wrist position

Out of all the different angles your wrist can be in with its ability for roll, pitch and yaw, there is only one position that has the most strength and stability, and that's the position you want your wrist to be in when making contact with the ball. If you wanted to punch something you would want a very solid, stiff wrist in order to not hurt yourself. Try standing in front of a wall and put your fist against it at shoulder height like you've just punched it; if you roll your wrist down on your forehand in order to compensate (similar motion as revving the throttle of a motorcycle), you've weakened your wrist strength. If you roll your wrist over on your backhand in order to compensate (similar motion as rolling up a blanket), you've weakened your wrist strength.

Why is proper wrist strength and position important?

Two reasons.... 1) because we rarely hit the ball in the middle of the racquet, with the racquet perfectly flush to the front wall and the swing perfectly level to the ground. The stronger your wrist when you hit off center, the less your wrist will buckle and the better your chances are of the ball still going where you wanted it to. And 2) you want your wrist to snap into that strong position when making contact, returning to a consistently repeatable spot every time you hit. If you're rolling your wrist to compensate instead of turning the racquet to switch grips, you are changing your swing every time hit, making it very difficult to practice and get comfortable with a consitent stroke.

I hope that all made sense! Please let me know if any of this was confusing, this is the first time I've tried typing out these mechanics that I've been teaching for years. :)

tl;dr: grip change is essential to keep good form.