What are sub actions?

With the use of the action event, you can select a previously created action or create a new one to execute as part of the action you're currently viewing.

To keep your application clear, avoid creating long actions, but instead, create multiple short actions that form a chain of actions. Especially when you're expanding your application, short actions are easier to maintain. Another benefit of short actions is that you can call upon them in great amounts and still maintain good performance in your application. This on the contrary to huge actions processing huge amounts of data.