Cutting wheels for the same diameter angle grinder can have different thickness. For example, 125 millimeters wheels can be 0,8 or 1,0 or 1,2 or 2,5 or 3,0 millimeters thick. I've tried several variations - looks like the thinner the wheel the faster it cuts because the smaller is the contact surface.
What's the reason for having so many thickness varieties of cutting wheels of the same diameter?