When creating a new user story map, you usually add steps and then you might want to add existing records like Epics and Features under these steps. But adding an existing Epic or Feature from the "Add existing records" panel will just add those items at the very right end of the user story map, and then you have to drag them over in a painful way.
It would speed things heavily up and make the life easier, if there would be an option to not only be able to create a new Epic or Feature when clicking on the "+ Add epic" tile, but also choose from an existing epic. (see attached image)