Using image sprites is sort of a last resort after you have done as much as you can with other optimization techniques. A sprite is an image that has all of your other images inside of it, so if your sprite has 10 images, you'd be getting rid of 9 HTTP requests and speeding your site's loading time up by the time for each of those 9 requests' latency.
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E. Arica, J. Strandhagen, and H. Hvolby. Advances in Production Management Systems: Innovative and Knowledge-Based Production Management in a Global-Local World (Part I), volume 438 of IFIP Advances in Information and Communication Technology, Springer, Heidelberg, (2014)