My current mentor, Ms. Massey is one of several teachers who were selected for a pilot program. The pilot program involves Massey using a set of hardware with one of her classes. The hardware set consists of a headset, a transmitter, speaker, and a handheld microphone. The transmitter is to convey a signal to the speaker so that when Massey speaks into the headset, you hear her voice from the speaker. The handheld microphone is for the students.
In my view, this microphone set isn't really for the teacher necessarily. In all the elementary classes that I have sat in, I have never thought, "I can't hear what the teacher is saying. I'm gonna ask the teacher to repeat him/herself." However, those are thoughts that I have at least each lesson with the students. Also, there are definitely instances during lessons when students cannot hear what other students have said. So, the microphone set is really for the students.
The thing with this microphone set is that the volume could be set so high that even if a student whispered into the mic, you would still be able to tell what they had said. Further, the likelihood that other students hear what a speaking student is saying also improves.
The aim of making students more audible to each other and the teacher is not necessarily simply to make them more audible. It's that when they are not audible, time must be taken out of class time to get them to repeat what they had said. If they are heard the first time because they are using a microphone, then they won't need to waste time by repeating themselves.
If you want to be hard on your students, instead of using the microphone, you can just skip inaudible students and move on to the audible students. That isn't something that I would personally do because I think that it would serve as a confidence killer.
Some kids are afraid to talk because they are worried that their ideas will not be approved of (to speak generally). If they are heard and their ideas are respected, then it's my conviction that those instances will build their confidence to speak in class. That's basically what I think a value of having the microphone set in a class is.