This would be a great plugin if it worked. I've got a complex site, and it's filled to the brim with categories; one alone manages old, no longer used categories (but ones I need to keep around, nonetheless).
Unfortunately, this plugin works (I imagine) with only older versions of WordPress. Installing this on a new version of WordPress will lead one to a database error, due to recent WordPress versions adopting a system that favors tags over categorizing a bit.
You'll receive an error similar to this:
WordPress database error: [Table '###.wp_categories' doesn't exist] SELECT SQL_CALC_FOUND_ROWS * FROM wp_categories WHERE category_parent = '0' ORDER BY cat_name LIMIT 0, 50
Hope this plugin is eventually updated!