This dialog appears when you have dragged and dropped one or several modules from one container to another in the Tree view in Controller view mode. It displays the module type(s) and the new location, where the modules will be added. Use it to confirm the moving of the module(s). Yes confirms the movement, No cancels it.
If you select this option and accept it with Yes, this dialog will not appear anymore in the future when you repeat this action. You can reactivate the confirmation dialog in the Tree view properties. By default, this dialog shows up.