We prefer to keep certain business logic and workflow actions in Flow and not in PowerApps. An example of this would be calling a Flow from PowerApps to evaluate conditions from various systems, and return a result or error to PowerApps for the application or the user to react on.
At the moment we have to set up a custom connector to Flow (HTTP request\response) to trigger the flow and return the result to PowerApps. This works extremely well, but it takes some effort to configure. The default PowerApps action to call a Flow does not have the ability to provide feedback to PowerApps from the Flow runtime. This would be a great addition for more advanced flows.