Google added a new Gmail Labs feature "Hide read labels," that when turn on, hides all your labels without unread messages under the "More" menu. Labels with unread messages will automatically show up, unless you've explicitly chosen to keep them hidden. “This’s particularly handy if you use your inbox as a to-do list where unread messages’re the outstanding things you need to take care of. If you use that method along with labels like "Home" and "Project X," it's easy to see all your to-dos in context. With this Labs feature on, labels with outstanding to-dos will be bold and have a number next to them; everything else’ll be hidden in the "11 more" section,” Gmail blog.