The system will execute a subflow depending upon where you place the Start subflow action.

Subflows can be added to a step. The subflow will be executed AFTER the step is Proceeded.

Subflows can be added to a connector. The subflow will also be executed after the step is Proceeded.

Add a subflow action to a step if you ALWAYS want the system to see if it should be executed (subject to conditions added).

Add a subflow action to a connector if you want to control which subflows execute depending on the path the flow proceeds down. So you may have multiple connectors to a step, and you are able to specify different subflows for each connector.

You can check the Lock setting for the Start subflow action if you want the system to wait until the subflow is completed before moving on to the next step.

Sub-flows can be used in any flow that shares the same data source.