Manual is used whenever you want to trigger an automation to start the application rather than simply calling Start on the adapter. This will trigger an event to fire from the StartMyDayController component that you'd respond to in an automation to connect to the automation you wish to use to start the application.
You might use this for a situation where you need to copy some files whenever you start the application.
You would use manual if you wanted to fully control the startup process for an application or multiple applications. An OnAdapterStart event will be raised each time an adapter is requested to be started and the adapter to be started will be one of the event args. Set up a separate automation that listens for this event for each adapter. In each automation test to see if the adapter in the event args is the one you are listening for.
I use this to allow me to slow down starting applications to prevent load on the computer and when an application has a specific start up process that isnt supported by Automatic (such as starting a text adapter with its companion WIndows adapter).
Here is a sample automation that will only respond if the Calc adapter is requested to start.