CPAN is the first place people look for an existing solution to a problem. One could perhaps post a WIP module to a website, but there's no guarantee that anyone will find it off a search engine.

As long as a module a) does what it claims, and b) is documented, my feeling is its good to have it on CPAN where people can find, use, and assess it.

Plus if the namespace is registered the meta data gives us the opportunity to state/see the development stage of a module.