Is it common to use sections of one image for multiple icons on your site?

While digging through reddit's source code today I noticed that most, if not all, of the icons on the front page were just sections taken from a much larger sprite sheet (http://ift.tt/1Th4uiK). Then by using CSS they use the background-position property to pick which portion of the sprite sheet to use. For example, this is their code for the styling of the upvote arrow:

.arrow.up { background-image: url(sprite-reddit.ZDiVRxCXXWg.png); background-position: -42px -865px; background-repeat: no-repeat; } 

Is this common for other sites to just have one image file but pull multiple images from it? I'm a noobie to web design so this may be common practice that I am not aware of.

Epic visual tool

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