If you set the WHEN condition to be Started by action, you turn the entire behaviour into an action that can itself be triggered by a action, either in another behaviour or in the same behaviour. It is to be used with the DO: Start behaviour action.

You can think of it as a nested behaviour which can be referred to by other behaviours, without having to write the same behaviour over and over again.

Example: I wish for two different conditions to activate the same behaviour.

One condition is states matching an order of switches, the other is a Variable reaching 5. Both will start the same behaviour with the Start behaviour action.