It would be nice, and make managing layers very easy, if on the details page you could list whatever maps they may be a part of. This would prevent accidental deletion as we try to conserver on server space. This sort of functionality is used in MicroStrategy, where as you look at the properties of a metric or an attribute you can see exactly what it is used with/in. Very handy to know.
This idea has been merged with Provide a warning about dependent items when deleting an ArcGIS Online feature service.