Big-scale hotlinkers may not realize how much they're affecting their visitors' experience, thereby harming their own site. Have you ever visited a page that was made entirely out of hotlinked images? Those things can take several minutes to load up-- sometimes to the point where I get tired of waiting and click the X button. You can watch the action in your browser's progress bar. If the images were hosted locally, visitors would get them all right away and they'd enjoy the page a lot more.