Modern Vespa

The fact that MSF teaches newbies to use a kill switch means less than zero to me. I really can't think of anything less consequential than how you turn off the engine. Do it however you want.
If I had to overthink this (and this thread seems to be forcing me to do so) I'd say it's simply more efficient to turn the key and remove it than hit a kill switch and then turn the key and remove it.
I've owned a lot of motorcycles. I like the kill switch that's a little red button that pops back up and don't prefer the one that you turn either direction and have to turn back. On more than one occasion I puzzled over why the bike won't start only to realize the switch needed to be moved.

Govt. Mandate.
There are parts of the world where motorcycles and scooters don't have kill switches, and the light switch has off, low and high beams.
I think most of the people who don't use the kill switch probably started on bikes that didn't have a kill switch.

Good point. My first three scooters certainly didn't.

I was told the same by my local Vespa/Piaggio dealer. So I always use the key.

Sure. But the manufacturers aren't likely to implement the kill switch in such a way that it harms the engine.

It's bullshit, though. They also probably told you to break it in gently.

Clearly, you have achieved riding nirvana and no longer need to be concerned with riding safety, nor do you need any advice thereof. You are thusly excused from this conversation.

P.S. the MSF Experienced Rider Course is a great skills refresher for experienced riders. But somehow I suspect you're not interested.

Using the kill switch in emergency situations and other situations requiring fast shutdown is the purpose of the kill switch, even more so when one cannot remove their hands from the handlebar. It makes sense to practice using the kill switch to form a habit and create muscle memory.

That said, I use the key to turn the scooter on and off in normal operations.

I have been riding since 1974, been through at least six MSF courses and one adventure riding course. I have owned/ridden bikes without kill switches. I have been down several times on the road, more off road, and been present when others have been down. There are times when a bike is on it's side and running, but the kill switch is very hard to reach as that grip is on the ground and the key is fastest to use. Conversely, the opposite when a bike is on the left side. There are times when one needs to shut a bike down before stopping, the kill switch works perfectly for that.

I don't see this as an either-or situation, rather situation-based. Like many things, practice makes perfect, or at least creates habit and muscle memory.

My first bike built in 1973, was exempt(grandfathered) from turn signals. Can't even remember if it had a kill switch.
This thread is fummy Me sa like it.

Is this not when you have 1 scooter more than you need?
I need both my scooters, so if I NEED one more scooter to reach nirvana, it could go on forever

I just put down the kickstand. Never got the killswitch habit, but it's certainly handy when you come off, which eventuality is as much a given amongst us free living two-wheeled knights of the road as developing those horrid age spots, if not the heartbreak of psoriasis.
Talk about instincts! After 50 years on bikes, I have discovered that on a scooter, stomping on the left side of the floorboard doesn't make the transmission do a darn thing. Don't ask me about the clutch...

I ride my '06 GT200 the same way I would drive an automatic transmission car. Release the brakes, and accelerate fairly rapidly until I reach the speed I want to go, or get close enough to a vehicle in front of me that I need to back off the throttle. When I'm done riding for the day, I park it on the centerstand. The next day, or whenever I ride it again, I start it up, and let it warm up for several minutes on the centerstand, then push it off the stand and take off. I shut it off with the key.

I also have a manual transmission Stella (same as a Vespa PX150) and a few manual transmission motorcycles. I have removed the electric starter from the Stella, so it is kickstart only. It also has no sidestand. I start it in neutral, let it warm up several minutes if it has been sitting for a while, push it off the centerstand, get on, pull in the clutch, shift into first, and take off. I tend to short shift the Stella, because all the gears are fairly low and you can short shift it without lugging the engine unless you are going uphill. You can actually take off in fourth by slipping the clutch a little, but that is not good for it. If I need to keep up with fast moving traffic, I leave it in each gear a little longer to accelerate faster. I shut it off with the key, and leave it in gear so it can't roll.

On manual transmission motorcycles, if they are cold, I start them up in neutral, let them warm up several minutes, then get on, shut the engine off with the kill switch, shift into first gear, then flip the kill switch back on and restart the engine in gear. For the rest of the day, it stays in gear. I leave it in gear and hold in the clutch at stop lights, and always park it in gear. I do not like shifting a motorcycle into gear from neutral with the engine running and the bike not moving. The gears do not mesh properly, and it puts a shock load on the engine and transmission. That's what causes that "CLUNK". Keeping it in gear at stop lights not only eliminates shifting into gear at a stop with the engine running, but keeps you from haveing to shift into gear if you need to move fast. I do the same thing with the Stella. Parking it in gear also works as a parking brake.

So the only time I use the kill switch is when restarting a manual transmission motorcycle for the second time, while in gear, after warming it up in neutral. I have never had to use a kill switch in an emergency, but I know it's there. A big issue with dropping any bike with the engine running is that the engine is running without oil. Most carbureted bikes will die almost instantly when dropped. Never dropped a street bike, but I have dropped a few dirt bikes.

Update for you.
I checked that when I turn the engine off while the Vespa is off the center stand that clang sound doesn't come. When I put on the center stand hold the rear brake & then turn of the engine no clang either, but when it is on the center stand and the brake isn't applied then the clang invariably comes, not 100% of the time but more like 99% of the time. I believe when it doesn't it is because s jimC explained.