Also there are times when you might want to throw the angle grinder into the water!
I was using one with a flap wheel when a clump of flaps flew off and the wheel was then so out of balance that the angle grinder started vibrating so violently that I could barely hold onto it. As I tried to switch it off, the only other way of stopping it seemed to be to throw it into the water and hope that the RCD worked. A fraction of a second before I did this, I managed to switch it off.
Two lessons: First, flapwheels aren't necessarily as safe as one might think and second, only use an angle grinder with a very easy-to-operate On/Off switch. I once owned a Hitachi angle grinder which required two hands to operate the miniscule switch. Never again.