Unless there’s some flaw that they’re not admitting to like a bad switch allowing the vacuum to start up unexpectedly, I’d wager that it’s just a caution against people tripping on it or kids playing with the vacuum and getting hurt.
Many moons ago we had an older cannister vaccuum at the cabin. I was up there alone during the autumn - black fly time. I have a serious issue with black flies, and rather than swat them, i just vaccuumed them up.
Forgot to unplug the vaccuum.
One power surge later, I was wiping fly bits and burnt vaccuum rubber from the walls. shudder
Again, it was an old vaccuum, but I won’t leave any vaccuum plugged in anymore.
Lots of products instruct you to unplug them between uses, such as toasters. I think this is a greedy and dumb way to try to limit their own liability by requesting unreasonably inconvenient tasks be done by others.
Speaking of unreasonable cautions about products, I have an MSDS for Borden’s Hand Cream that says to prevent prolonged contact, and one for rubbing alcohol that says in case of skin contact see a doctor (the last doctor I saw put some on me). A favorite is the warning on a Q-Tips box that said not to insert the product into the ear canal, but only use it to clean the outer ear (where fingers and washcloths already reach fine).
I did read a funny story about a guy using a big rented floor sander. It blew the circuit breaker, so he went downstairs and reset that, and heard a whirring overhead and then a crash at the far end of the house. Not thinking to turn the breaker off, he ran upstairs to turn the sander itself off, and found it had made a nice start on digging its way into the basement.
On the packaging of microwave popcorn: “Contents will be hot after heating”. sigh
Anyways, I want to hear more about the exploding (imploding?) vacuum. We once had a townhouse where they insisted we umplug the AC wall units even though they had a switch on the cord in addition to the on/off switch on the unit. Never figured that one out.
What about lightning damage? I have seen modems affected by lightning storm. Oddly I’ve never seen a computer damaged by lightning, but I’ve seen DSL, Cable and Dial up modems effected after big lightning storms.
In that case it may be the telephone cord or cable cord not the electricity that’s effecting it. You can turn the computer off and if it’s anyway connected, you can fry your modem.
So perhaps they are thinking the same thing or maybe it’s a hang on from the days when electricity wasn’t grounded as well?
I recall in my youth installing toliets for my house and it was said not to use a toliet during a thunderstorm due to potential shocks.