It would ease development in some situations when you are making two apps but want similar functionality from the other app. Now it is impossible to copy controls from one App to another App with all the functions.
If copying multiple items form one App to another App was posible to do in Web Client it would be awesome.
Excited that this feature is now complete! You can now copy and paste across apps using Ctrl+C to copy and Ctrl+V to paste.
Read more here:
https://powerapps.microsoft.com/blog/copy-and-paste-controls-across-canvas-apps-available/