The main advantage is that all pages are in the view of the browser. Also, the pages are listed with relative equality; pages near the top will be given more importance. You can randomize the sort order to get around this.
The disadvantages are numerous. When a site gets too big, this can take long to generate (especially if it is randomly sorted), and very long to read. It's completely flat, so you lose the main advantage of using a hypermedium: organization of information.
However, that being said, it's nice to have this feature in conjunction with other IndexingSchemes.
There is now an AllPagesStandard.
A list of wikis' implementations, useful for MetaWiki or TwinPages implementations:
And, of course, a WordList.