A guitar players best friend. It allows tablature to be played back which decreases the amount of time it takes to learn a song. It can also be used to compose midi music, or convert a midi/tab into musical notation for players of other instruments to read.
Bill: Dude, I'm trying to learn eruption, but it's so fast i can't keep up with the tab
Ted: Try power tab, bro
Bill: Oh man... I'll never go back to tabs again.. This rules.