dadgad; is very useful for playing in d and g. you can get modal chords;such as ddddad or daddad thEsE inversion ARE impossible[ OR VERY DIFFICULT] in standard tuning. although you can get a d modal in standard, although your invesions are limited. THE PROBLEM WITH DADGAD is if your tune modulates[ changes key]it can become awkward
   personally as I sing in a minor, a major,c major I PREFER STANDARD TUNING[ OR DROP D]For d major.
   DGDGBE is useful if you put the capo on the seventh fret and capo just across the top 5 strings, you can pick out a high melody with two d s in bass . A guitarist I was playing with recently told me a minor is awkward in dadgad, Ive never tried it becauase a minor is brilliant in standard.