Some sites and forums will allow users to upload content like videos and images to the site, which will then be hosted by the site. I know some sites that don't do it, because it takes resources or bandwidth from the site. I'm sure some hosts limit the amount of user storage, but I think it's great when a forum especially, allows users to upload content so they don't have to host it themselves. But I understand if it's a bigger site, it might be a problem letting a bunch of people upload content to their servers.
