Open strings can open a lot with your audience
Open strings are one of the most beautiful things about the acoustic guitar. When they ring clear and true, they can open the ears, hearts and even the wallets of your audience.
You can find the greatest resonance from the instrument when you play open strings. Technically, the moment you place your finger on a fret of the guitar you are limiting the sound. Yes, fretted notes can sound great, but they will never give the sustain we get from playing open strings.
Open strings, open keys and open tuning
There is currently a lot of interest in alternate tuning approaches for the guitar. It's a way to use more open strings. But we can also do some organic things to get more open strings going.
When I wrote my song, Breakfast Blues in the key of Eb, it was a great blues key and worked well for the vocal, but the accompaniment just didn't carry the song. I changed the key to E (natural) and it opened the song way up. The new key with all the options to use open strings created opportunities to develop a broad accompaniment that really filled out the sound.
I also used chord voicings that enabled me to use as many open strings as possible. I was able to have an open E string "pedal" throughout a few sequence of the chord progression that provided some interesting harmonies as well. This supported the vocal more fully and gave the song a much bigger sound, which is always a challenge for those of us presenting material for guitar and voice alone.
Moving the key up a semi-tone was a bit harder on the vocal and I'm still improving here, but the extra work will pay off. So if you find your fully fretted chords are not giving you the sustain you want, you can try a different key. Also try to experiment with adding some open strings in parts where you might not normally use them. Your end result will be to open the ears, hearts and if you are lucky, maybe even the wallets of your audience.