Last year several people were recommending this approach and reporting "success" from their point of view.
However several Google sources have made it clear that Google doesn't want that. The Sitemap is supposed to be only those URLs that you do want to see indexed. I'd say there should be no concern about Google "losing" URLs - especially URLs that have been crawled recently. Google doesn't seem to forget a URL ever! So I've always gone with their direction and the results have been fine.