Basic blender went bad (motor ran but spindle wasn’t rotating). I wanted to disassemble to see if it could be repaired. Three of the four screws were Phillips head. I had to cut the casing open in order to discover why I couldn’t unscrew the fourth. It was a slotted spanner.
Grinding a notch into a flathead screwdriver is annoying but it’ll still work fine as a flathead even afterwards. I would probably just grind the bulge out of the screw though.
In this case the screw was at the bottom of a narrow slot, and they only found it after breaking things.