I understand the purpose of namespaces, to break up the global namespace, and I can understand how they would be extremely useful when working with a large team of programmers or integrating several code bases. But when you are the sole developer on a project that you are writing from scratch, what is the value in encapsulating all or part of it in a namespace? I keep reading about how important it is to organize into namespaces, but unless I'm writing a library that someone will be importing into a different project, I don't see the point. Can anyone enlighten me?

The major reason to use namespaces is to prevent naming collisions. Say you have a rendering engine that does both 2d and 3d. So we have two point structs, one that is 2d (x,y) and the other 3d (x, y, z). The easiest way to deal with this is within your engine have a 3d namespace and a 2d namespace, that way you can easily know which point you are using.

theTroll

Like the others have mentioned it's to avoid name collision. And if you're using any sort of libraries then you'll probably want to encapsulate your modules in namespaces.

An example of something I used today at work (which is kinda ugly, but that's life when you're working with legacy code):

ModuleA::Team& moduleATeam = ModuleA::GetTeam();
MyModule::Team& myTeam = m_myModule.GetTeam();

Without using the MyModule namespace the reference to Team would be ambiguous and the compiler wouldn't be able to resolve the symbol.

Essentially I find that it's good practice to put all your sub modules into their own namespace (with good descriptive names) to reduce the risk of name collision problems. Doing it right off the bat is much easier than retrofitting your code to do it later.