- fuller, deeper, stronger tone
- higher tension when you tune to open tunings, such as Open D, Open G and DADGAD.
The problem, I found, is that it takes a while to remap all the chords. That remapping process takes a little time: The G comes up and rather than going "G! Got it!", you're going "G. The guitar is down a minor third, so to get a G, I have to move it up three frets. Can't be an open chord, so we're thinking Bb, which is here!" Problem with that, is, by the time that thought process has happened, you should be playing the next chord. And you haven't remapped it permanently and completely yet, so the next time the G comes around, you might or might not have it memorized. And again. And again. Next song, it might or might not be the same G. And, if you're jamming with friends or simply playing "Guess the Key"* with the radio or your playlist on random, this is fine. But if you're playing in front of people, it's really not a good time to start trying to find your G chord. It makes you look and feel like a rank beginner, which doesn't feel good when the tempo is passing you by like truckers on the interstate.
Definitely a good idea, but you have to learn to live with it a while before you can gig like that.
* "Guess The Key" is simply this: You start a song, preferably a song you don't know. It starts playing and you start trying to guess the key of the song (e.g. "A" ), then you start trying to piece together the chord structure ("A D F#m E") and finally start trying to figure out something to play over the top of it. One time, I had the Sirius "Outlaw Country" channel on, and I went for a lick and heard the session guitarist go for the same lick. This is a good exercise to develop your ear and your genre-related knowledge.