Not to mention eliminating the risk of firing a ball round into the grenade.
One interesting fact is that some modern rifle grenades can be used with ball ammunition. Just slip the grenade over the end of your standard NATO flash hider (like one you might find on an FN rifle) and fire with standard ammunition. A “bullet trap” at the base of the grenade catches the projectile and carries the grenade away to its fate. Then your rifle is ready for regular old shooting with no magazine change or gas-port opening or anything.
I believe MECAR of Belgium makes these grenades (all the cool stuff is made in Belgium).