Well, the M&P doesn't have a hammer, but you're correct.
The larger beaver tail is intended to give a more positive grip when speed is a concern. It is there to guide your hand as high as it can go without getting hit by the slide as it comes back.
It's not as pronounced on the smaller guns to help reduce the possibility of printing when being concealed.
You could grind it off. It will not affect the function of the gun if you do. However, it will hurt the resale value of the gun should you ever try to sell it.
Agreed to what everybody above said. There are companies now that make aftermarket beavertails for Glocks no. Personally, I like it (the M&P beavertail that is. I have no experience with the Glock ones).
I shoot IDPA with my 9mm pro and I love the beaver tail on it. It allows me to get as high and consistent grip as possible when I draw from the holster.