Makes them more easily accessible throughout the shell.
Should it purge the entry from kactivities stats when you manually remove the download from the download list in the browser?
Edit: Looks like the chrome.downloads.onErased signal doesn't fire for me, and even then, I only get the ID of the item that got removed, I probably can't query it for the filename after that.
Makes sense to me conceptually. Speaking personally, I would benefit from this as I often want to immediately do something with a file I just downloaded. Often the notification pop-up suffices, but if I want to do that thing more than a few seconds afterwards, this is a good thing to have so the file appears in the recent docs list.