Actually, you can never physically see frame rates faster than your monitor's refresh rate anyway. Regardless of whether or not Vsync is on. Vsync just forces the video card to keep reported fps within the boundaries of your refresh rate. It also prevents the tearing and artifacts and such that you noticed. What happens is the video card gets so far ahead of what is actually being shown on the screen that it has to pause to allow what is actually being rendered on the screen to catch up. If the CPU happens to be under a heavy load also, you'll get little freezes and warps and screen tears because things get out of whack.
People like turning it off because it makes them feel good to see big numbers on their frame rates. They think they have gained some sort of performance increase.