You can make the flip side usable or, if you’re bad enough at it, both sides unusable.
http://www.catb.org/jargon/html/F/flippy.html
You could use a hole punch to make another write notch on the other side of a single-sided floppy, doubling your disk space (though at the time most drives could only read one side at a time).
Some disks were also shipped without a write notch at all, so that you couldn’t replace whatever was on them; a hole punch gave you a free reusable floppy!
Some manufacturers insisted that the back of a floppy wasn’t good or whatever, and I think in the *very* early days some of them weren’t hard-tracked/sectored on the back but by the mid 80s I’d’ve bet it would work on any of ‘em.
…I can *smell* 5.25” floppies in my memory now, sheesh.
Vancouver Island != Vancouver.
https://www.town.lakecowichan.bc.ca/scenic.php