CONAries said: "Genrally speaking microphones should be used in musicals due to the orchestra, however, I personally feel there is no reason why ANY play should use microphones! Any trained actor should be able to project their voice throughout a theatre."
The problem is that a lot of them can't. Especially the ones who come from Hollywood and are used to close-ups. Personally, I would rather have mikes than have to struggle to hear what some actors are saying.
I remember attending an unmiked performance of Plaza Suite a thousand years ago. George C Scott had left, I believe unexpectedly because I expected to see him, and he was replaced by Nicol Williamson, a highly acclaimed actor. Maureen Stapleton was a wonderful actress who, to me, always seemed to be shouting a little bit to make sure her voice carried. As great as she was, it sometimes took her out of character to me. Well she was onstage with Williamson and, not once but twice, two different people in the audience yelled out 'louder' because they could not hear what he was saying (I couldn't either and I belie e that I was still in my teens). His failure to project, coupled with her tendency to shout, was jarring. I still remember that 50 years later. Had they been miked a bit, the performance would have been better. Can think of other cases, but that was the most memorable.