Apple GarageBand is an application that has been allowing aspiring musicians to record their noise-routines and organize them into a homegrown track that can be ignored by the music community at large since 2004.
Simply put: GarageBand exists to nab the "artsy" demographic of prospective computer purchasers who don't really have the time to fuss over a real computer (their time is better spent working on being irrelevant). GarageBand also serves the purose of being an excuse as to why your band's tracks are so iffy. As in; "Dude, bro, our band does not suck. We just don't have the money for real recording equipment and had to use my sister's Mac to record our demo. Give us a break; we're trying to make it, man." Though the band in question may indeed suck, they were able to divert attention from how terrible they are using the excuse that their equipment is sub-par, thus increasing their cred as a band (they're struggling, does it get any more real than that?) and includes the added benefit of not having to admit that they should totally kick out their singer becasue, lets face the facts, he's just not on the level that the rest of the band is. GarageBand works on multiple levels and satisfies a broad range of duties demanded by the modern "starving artist" scene.
A plethora of things! Have you ever wondered what it would sound like if you could actually sing in a tolerable pitch? GarageBand has auto-tune for just such a desire. Have you ever wanted to make a generic and repetitive beat while you and your cacuasian friends mumble verses in a slap-dash attempt at hip-hop? GarageBand has the loops and beats you need to keep it hood. If you're passionate about music but spent all of your recording equipment money on a Mac, GarageBand is pretty much your only choice. As long as you have a desire to record the noises you bang out GarageBand will be there to assist you in recording a decent imitation that is vaguely similar to what you had in mind.