Hi Doc,
I think there are several reasons. The three that I can think of at the moment are the following:
1. Open tunings are great to simplify chord positions for your fingers. I remember James McCormick sent me a link to a website about one of his favorite artists Richie Havens who uses this tuning because it's chord formations. Check it out on this thread: http://www.chordie.com/forum/viewtopic.php?id=5471
For example, to play any major chord, all you have to do is bar the fret (open D tuning, barring 2nd fret = E Major Chord, barring no frets = D Major chord)
2. I recently got into Acoustic Fingerstyle and I noticed that a lot of artists who play this type of music (Andy Mckee, Kotaro Oshio, etc...), use open tunings in a lot of their songs because they allow them to perform all types of techniques (slapping, tapping harmonics, slide), without having to compromise the tonal quality of their music. In open D, doing slaps gives a rich aggressive tone and doesn't require difficult chord formations. This allows them to focus a lot more on their actual technique rather than trying to remember complex fingering.
3. For the sound. Try tuning your guitar to Open D (DADGAD), and transposing the chords of a song you know to this tuning. You'll immediately notice that the "bass" strings give a much deeper sound and therefore add a different quality to your music than if you were in Standard Tuning. I like playing around with different tunings to find a sound that compliments my music in a different way.
In any case, I would definitely recommend you to experiment on your own. At first, I was reluctant but I can say now that it helped with my music in different ways, mainly with my understanding of music theory in general, as well as opening my mind to different ways of playing. Here are a couple of pieces by some great artists played in Open Tuning (you can find videos on youtube):
- Andy Mckee - Drifting
- Kotaro Oshio - Wings (you are the hero) - This one's a blast to play
Enjoy,
J.