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 an 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.