We delete files all the time to free up space, or to get rid of pesky evidence, but the whole process is a lot more complicated than it seems from the outside. When you go to "delete" something, you're just pressing the start button on a much more involved, much more random process. So what actually happens to that data?
As Vsauce explains, "deletion" doesn't have as much to do with destroying a file as it does with removing the protections that keep non-deleted files safe. And over time, your system washes old data away like so much silt. Of course, sometime's that's not good enough, and then the process gets a whole hell of a lot more complicated.
Anybody have a sledgehammer I can borrow? I've got a little cleanup to do.