To put it simply, as soon as you make more than one web page you probably find that there are certain things your pages need to have in common in order to make your readers' navigation easy, and to make their experience pleasant and consistent. Perhaps you want all your pages to have a similar look, with the same logo at the top of each one. Perhaps you want to show an outline of your entire site, with links to all the different pages, a kind of live table of contents. Implementation of these and similar features is exactly the sort of chore which, while tedious for a human being, is easily automated by a computer.
Manila lets everyone who works on a site focus on what they do best.
Finally users can do simple edits on their own sites. Overworked webmasters are no longer a bottleneck. Communication within an organization and with the outside world improves. The team gets on the web, without the pain or confusion associated with more traditional methods of managing a site. Engineering for this site, provided by The Office of Larry E. Reider.