A lovely thread. I've sung in all kinds of configurations-- unaccompanied, accompanying self, others accompanying-- and enjoy it all. But some of my best memories are of singing in the car on long trips with my family, through snowstorms singing Chritmas carols for instance, and I think that's one of the reasons I like singing without instruments, but with others.

It's true too, as someone said, that singing is a very sensuous experience, the way that it feels in the body, and that can best be felt when singing alone because your attention is totally on the experience and you don't need to think about what your hands are doing or about anyone else's involvement, though there's a different kind of excitement to the experience when it is shared, especially with another singer(s).

I also agree with everything GUEST,RUSS said. Well put.