DADGAD became a means to an end for me when I started playing guitar accompaniment to jigs and reels. Most of this can involve hopping between the keys of D and G. The standard tuned guitar chord of D is particularly weak as a strummed chord. It could be argued that G to leaves a lot to be desired. DADGAD is not the answer to everything, but for me it unlocks a lot of doors and enables me to explore the whole fretboard.
If anyone is interested, I will be at Roger's Rant in Milborne St Andrew, Dorset on the 8th, 9th and 10th July. Lots of sessions, dancing, workshops etc and all for worthy causes!