It is indeed almost never needed. But you probably have multiple sub microflows that need to be called. So you could use this boolean to validate if all the submicroflows did their stuff and do some logging otherwise.
It is used to indicate if something couldn’t be setup correctly when the application was initialising.
For example, if the Deeplink module failed to initialise, then any deeplinks you have in your application won’t work. You need to decide if this is a fatal error in your application or not. If it is, return false in the after startup microflow and the application won’t start and you’ll get an error. If you return true, the application will still start, but with potentially broken functionality.