Why not just write to USB directly?

cp debian.iso /dev/sdX

Because one single character typo and you just wiped out your system drive or some secondary HDD. It’s much safer to use a tool like Etcher.

I’m glad it worked. I was going to to rebut all the pessimists in here, saying I’ve done this before, and most ROM copies are identical. (Sites like Retro Achievements rely on ROMs having specific hashes, for example.)