Moderated versus unmoderated tests
In a lab, the facilitator sits next to the user, who will read the tasks, and help if the user gets hopelessly stuck, for example, if the Wi-Fi is not working, the lights go out, or the recording software crashes. For remote tests, the user encounters the facilitator as a voice. This voice can also read the tasks and help with fixing technical issues.
The main purpose of the facilitator is to ask questions; to explore why some things are harder to understand. The facilitator observes the test. They should not interfere with the user's natural journey--well, unless the user is stuck, lost, or has technical difficulties. This can be hard, especially if the facilitator is attached to the solution.
Note
The facilitator should not take notes during the test. This is why the tests are recorded. Moreover, the observers can take notes, and sometimes even transmit their questions to the facilitator. However, if the facilitator takes notes, their attention is split...