As a user of such sites, there is only one answer -- Windows. man perldoc is unavailable, and because the only Windows pager is a broken version of more, searching within the perldocs can be very annoying. I'm not allowed, at work, to install Cygwin or any kind of web server, so generating the HTML docs has met with limited success (file:// sucks).

So, when I need to search perl docs, I use an online repository. Them's the beans. As far as CPAN, I like being allowed to read docs before downloading the modules.

The nice thing about the docs on perldrunks is that they can be downloaded for offline use as well.