On a parking lot with a fence and barriers, controllers can be deployed without appointment. (Here we are therefore talking about people who give directions without training and appointment) (This concerns a private property). The road authority (municipality/province) determines for its territory which authority is required to regulate traffic and whether traffic regulation is required.
From an organizational point of view, this task does not fall under events. Traffic controllers who are deployed on public roads do this from their main task (as an employee). This requires the authorization as a professional traffic controller. Event traffic controllers may only be deployed during events and by the instructions of the municipality. The municipality will decide whether this is desirable/mandatory.
Event traffic controllers are exclusively volunteers and can only be used to perform light traffic control tasks in support of the police. (So no company employees can be deployed for this). Acting independently as a traffic controller is reserved for professional traffic controllers.