What does the switch "Disable resource leveling" mean?

In the Project Planner App

resource levelling switch

By default, Can Do's Watermodel balancing procedure is used. This simulates how the resource can distribute its work among all the work running in parallel so that times and quantities can be met.

This video demonstrates the procedure:

If the switch is set to "Yes", the adjustment does not take place. The resource is scheduled on a fixed daily basis with the average of the allocation over the package length. This increases the risk of overload.