I regularly share folders with clients and people I'm collaborating with. Especially folks within corporate organizations usually have now dropbox account and are working on smaller screens or laptops. Opening a dropbox link on that confronts you with at least 3 pop ups or bars for logging in, which all stand in the way of the content I want to share.
Similarly for the banner on top for which I integrated my branding. As it's a relative banner that scrolls with the content, using it on a smaller screen means that it's in the way of the content and files.