I sing both accompanied and un. I'm lucky in that I have a group of musicians I used to be in a band with who come to the same sings that I do and who will assert the key they know I prefer to sing in.

But here's the thing. I have a very good voice. I practice a lot. I pitch songs not at whim, but because the key I'm using the the one key that best enables the nuances of my voice to create the sound I want to create. If someone wants me to re-pitch, it's not that I wouldn't if I could; I CAN'T and use my "instrument" right. It would be, to use a musical analogy, like playing a harp whose strings were closer together than the one I usually play...yeah, I could probably hit the basic notes of a tune, but I couldn't do the decorations and flourishes that make my playing MINE.

There's something else, too. It's hard to explain, but some singers have a knack for implying a chord while singing one note. (Listen to June Tabor singing unaccompanied for a good example of this.) I can sing, say, an E and there are undertones -- colors -- that creep in identifying the underlying chord as an A minor, an E minor...this is complicated by the fact that I think in harmony and REALLY like to use rather unusual chords for emphasis. So if I'm singing that E and trying to imply an A minor seventh, but (since this hypothetical song is in C) a nearby guitarist opts to play the C chord that most folks would use at that particular place in the song, it sounds just dreadful.

So at a singaround, to forestall that guitarist I might say "This song sounds best unaccompanied" BEFORE I sing that type of song. If it doesn't seem to be the kind of gathering where that'll work, I'll forget about singing the sort of song I've just told you about, and launch into something accompaniable instead (or do a sea chantey, which usually isn't guitar fodder).

Cheers, Claire