what is the benefits to use image sprites in web site ?
I asked Google.
First result is not bad, second css-tricks.com/css-sprites is explaining it very good.
Sprites were intended to increase download speed by having all the small images together into one file, instead of spread out into multiple smaller files where the browser would either have to start and finish downloads for each one, or try to download them all simultaneously.
Note that sprites sometimes break with zooming, increasing/decreasing text sizes, and increase/decrease in display DPI. For that reason, I can't say I really use them any more.