Way back when, I had a simple hobby site where visitors could upload an image, I'd process it and return a transformed version of it in a template for papercrafting. Nowadays, I'd do it all client-side in javascript, but that wasn't really an option at the time.

So the images were saved when they were uploaded, not for any nefarious reason, but more out of laziness. Then one day, I looked at the images. Yikes. I immediately rewrote it to delete the images after returning them, and pretty soon let the site die.