When I was a kid I liked to poke around executables in the MS-DOS world. Hex editors were limited in the sense that they wouldn't let me insert bytes into the file, just edit existing ones. Because I didn't have access to an disassembler or an assembler (they were sold at stores but they were too expensive for me), I wrote a simple program that would convert a binary file into a text file full of hex codes, then I could edit that, change jumps to different addresses, change strings, and then I would reassemble the executable with another program to see the effect. I used this to translate programs and games to Spanish by changing the strings in the executable. Messages in Spanish are in average longer than English ones, so I couldn't just use a hex editor.

It's funny to me that the hex file format is a real thing.