I play in two bands. In one of them, I have put a ban on two things: using instruments that cannot simply be carried (like drum sets or pianos), and using amplification. Or maybe a ban is too big a word; I continuously make it clear to my mates that I am radically opposed to both.
And in a way I am. One of the reasons is that the singer in this band is a great communicator with any audience. But using a microphone would, I am convinced, put up a barrier between him and his audience. Using a microphone, one is often tied to a cable; but even when wireless, microphones make that one has to start thinking about singing-through-a-microphone-technique. Also, one can’t sing and wave both hands at the same time (very important), or grab a member of the audience by both shoulders if necessary.