Formatting a transparent HDD

Have you ever formatted your HDD and forgot to back up important files? Why was it possible to recover most of those files? Well, the "quick format" just erases the "where are the files", not the content! However, a full format will take longer (this time it was almost 2 hours!) AND it will mess with the data too! ... https://www.youtube.com/watch?v=RiuHbdwjglw