@AlexandreMasson-2318 Behind the scenes, the scale controller monitors sources for events/messages to decide whether to scale a function app out by adding more instances. This is usually achieved by polling the source which counts towards pricing/throughput depending on the service.
If you have an Event Hub or Service Bus that doesn't have a constant in flow of messages, you could switch to using the Event Grid trigger which triggers the function app only when there are messages with no active listeners.
A beneficial use case for this could be for dead letter queues that need listeners only in case of failures.