I sometimes download a file (which I think is okay, reading its title) and then after opening it, it appears to be a link to some sexprovider (of whatever you call this) with disgusting movies. For me that is JUNK ('cause I didn't ask for that, based on its title/name) and so I mark it as JUNK. When I want such a video I'll look for it. I don't want these type of files be forced upon me.
By the way, such a file often appears under a different title/name but with the same number of bits. Then I know enough......