GarageBand allows you to mix and create your own music tracks and podcasts. Finally, your dream of becoming music celebrity is possible with this program. You can create music to share with your friends and family members. The program will help you fix your timing problems, help you correct pitch, and add beats and sounds to your track.
Well, since the program is a part of iLife package, I would assume its primary use would be to add a soundtrack to your movie made in iMovie or slideshow made in iPhoto. On the other hand, you can create podcasts and broadcast yourself to the world for practically free (the iLife package costs you around 50 bucks).
A great benefit of the program is its musical instrument lessons. If you have a passion, you will get yourself to learn a music instrument or a couple of them. If you have a talent to come up with new music, then you could potentially create tracks underground, be found and become famous... like Mike Posner did, for example. I am not sure what he is using, but I am sure, he'd definitely check out the Apple's GarageBand software package.
So the bottom line is that the program has got a lot of cool features and a lot of benefits, if you use it correctly, because remember: "With great power, come great responsibility"! If you decided to buy this package to form your own garage band - go all the way! If you bought this packet to make a cool video and then burn it on a DVD or share it using iWeb - go all the way, make those dollars worth it.