The ordinary Latter-day Saint sacrament meeting is a service of assigned talks: two or three members are asked in advance to speak on a set topic and do so from prepared notes. On fast Sunday that programme is set aside. After the sacrament, the meeting is opened, and any member of the congregation who wishes may walk to the front and speak. There is no vetting, no time limit beyond the courtesy of the room, and no clergy in the usual sense to shape what is said.
What people say in these testimony meetings is a genre of its own. Some bear witness of belief in a few formal sentences. Others tell a story about a week, a job lost, a diagnosis, a child, a debt paid by someone who never said who they were. Children are brought to the microphone by parents and whisper a sentence. The meeting can be moving and it can be uncomfortable, and Latter-day Saints will readily tell you about the occasions on which someone used the open microphone to say something the congregation would rather not have heard, which is the unavoidable cost of an open microphone.
The practice matters structurally as well as devotionally. In a church without a preaching clergy, the monthly testimony meeting is the one regular occasion on which the congregation hears its own members rather than an assigned lesson, and it is where a ward finds out what is actually happening in the lives of the people sitting in it.