Provides very useful information, especially when you have a lot of widget areas. Foolproof.
I suggested that the author to add a toggle so I could easily show or hide the widget area names without activating/deactivating the plugin. (That would make it easier to visualize.) He added the toggle to the top admin bar. It works even better than I expected. Now I can see using this on all my WP sites in development! Thanks to the author for his responsiveness! Now I'd give 5+ stars for this simple plugin.
This is especially useful with Headway Themes and other themes and plugins that allow many placements for widgets or conditional placement of widgets and sidebars.