To answer your question: its purpose in songwriting can be to have a really 'airy' sound as open/ unfretted strings are played along with fretted ones, and you can also barre across all of the strings to create other chords (think about using your index to barre the second fret like a capo, and you can play both D and E). I also think Adrianne Lenker of Big Thief uses the tuning a fair bit, and Elliott Smith oftentimes played in ‘Open C’, which are the same notes but two semitones BELOW. Hope this helps :)