Use of icons has become more prevalent with mobile and app design; alongside progressive disclosure and audience overlap (both in regards to age and language)
Creating icons successfully is very skillful (having variations for different sizes being a subtle in itself). Using them in projects and wanting to change colours normally means taking them (or the sprite) into an editor—fiddly at best.
The above example (with just
color attributes changed) is using the Font Awesome, which makes application a breeze. No more images—even for social icons! (love the github icon—won me over)