This is a massive time saver. Firstly, Webflow only deletes unused files, so you can select all and delete, then republish your site, any assets being used are automatically added back in.
Plus, there are times when a site is duplicated to use as a base site for another version, that situation is also a great use of selecting all and deleting.
Anyone who has ever had to clear out a complete set of site files one by one will really appreciate this. 