I sing unaccompanied because there are instrumental numbers that don't require words, sometimes the words don't even matter, take Enya, or Scots Gaelic 'mouth-music'.

I also sing unaccompanied because it doesn't take up limited seating space with guitar cases ... if you have a decent singing voice use it, avoid pubs with carpets and heavy curtains.. there's no 'fold-back' as the mixing Engineer would say, and the song is acoustically flat....
I remember going to see Kate Rusby in the early days, her voice stood out, then later she added 'the wall of sound', I really went to her concerts for the odd 'minimalist' numbers she did, on some of the numbers she was drowned out.. but then it was a band and they all had to display their various instrumental talents and have a 'sess'..
... You can't do a wall-of-sound number with one voice, and a one voice number shouldn't have a wall-of-sound..... if you listen very hard, the song will come to you at last....