Purpose of DAA tuning
General mountain dulcimer or music discussions
The good news is that the Key of "D" major and its various chords are the same regardless of which tuning you choose as your primary tuning. If you play from tablature, the fret numbers will be different, but the musical notes won't be different. Two people, one tuned D-A-d and the other tuned D-A-A, can play together rather easily. However, if you play from tablature or chord diagrams, you are better off sticking to one tuning in your early stages of learning.
If you decide to play without tablature or chord diagrams, you won't even have to change your tuning to match those with whom you play. As long as you both are playing in the same key, you will sound just fine. After all, guitars, banjos, mandolins, dulcimers, etc. can and do play together without being tuned exactly the same. In each case, the musician is using his/her knowledge of their instrument to play in the specified key.
Just sit back and enjoy the tuning you have chosen. If you decide to explore different tunings at some point in the future, your skills will easily transfer.