Depending upon the size and configuration of a venue, some amplification, by way of microphones, might be in order. Many of the old coffee houses I visited in my youth were quite small and intimate. Amplification was usually totally unnecessary since the performers were within just a few feet of the audience in most cases.

I love the sound of unamplified instruments when it is possible to hear them, and the singers, clearly. I'm in favor of whatever accomplishes that for the listener.