I was on a Web site recently, saw that it was a good reference site, so I "starred" it in Chrome and added it to my bookmarks list. A few days later, after having spent a lot of time on another project, I couldn't for the life of me remember the address to that site. Then it hit me and I had bookmarked it.
Now, I could have clicked the menu button, hovered my mouse over bookmarks, and clicked the bookmarks menu item in order to open the bookmark manager.
But that's not nearly as efficient as typing chrome://bookmarks my address bar and pressing Enter. Doing so opens the bookmark manager.
There are actually quite a few Chrome URLs. A while back (January of 2013, actually), I posted about Chrome URLs and their usefulness. If you want to see the full list, simply type chrome://chrome-urls in the address bar.