Currently when you're cleaning up a project, and want to delete Line Styles, Revit will not warn you if this Style is still in use. Thus resulting in views with black thin lines (and no way of knowing what the Style was or needs to be).
Currently we're forced to open and check every view, or just delete the Styles and hope for the best.
Either Revit should give a warning that this Style is still in use OR it should give you the option to change the lines to another chosen Line Style (preferred solution).
Same should be done for Line Pattens, so you don't have to check all your Object Styles, Graphic Overrides,...