Delegation and shared line appearance gives us the ability to manage the calls the same way we used to with Manager/assistant filtering. It misses ergonomic intercations. This could be added to Calls app or into a separate app. It's mostly for delegates, or assistant. They need to see if the line settings of the manager or to transfer call to them, or somebody else. And to be able to change this easily, they need to switch the manager line forward setting from delegate to none, end reverse, really easily, as they would do that multiple times per day (for breaks, meetings etc..)
Going to the settings to modify that is not user friendly, process is heavy and settings difficult to access.
If this was available in an app, it would be much easier for assistant to see the manager line status, and change it.