Originally Posted by Frownland

It's because it gives you a more natural sound. While the sound hole is used for projecting the guitar body's tone, a lot of the guitar's timbre comes from the way that the whole instrument vibrates. The second mic also picks up inflections such as string scrapes and tapping better than pointing it at the sound hole. If you're the kind of person who likes to play the headstrings, then it will pick that up better too. You can also isolate the different sounds of the guitar later on in mixing. There are many factors though, what is your recording space like?

If you're into it and want to create a great record, just pick up a mic and use that. If you have a smart phone you can get a free app and a $10 aux mic. Be creative.