a frame rate of 60 (75) is good enough for any game, the main reason is ..
The display on the GPU card is achieved via 'block switching' display areas in VRAM. If your frame rate gets to high, the graphics (and cpu) processor does not have enough time to calc and draw all the info, thus never completion it's intended operation, streaking (or incomplete drawing) will result.
Slowing the frame rate gives the GPU enough time to draw the image and maybe more. Also a minor effect would be to keep the GPU processor cooler as it has a 'rest period' between frames. It'll last longer this way.