Its legislation tick box..........
I always have a spare generally on a car, but I know what to do with one (well, on cars where a spare fits!)
The standard approach these days is to get breakdown in.
In fact people call the breakdown for anything, its not unusual to see a roadside assist for low washer fluid!
There are cars that have a spacesaver spare, but the wheel you take off doesn't fit anywhere sensible. The mk1 TT and Beetles are like that. You have to put the original wheel on the passenger seat. Porsche 911s are similar. The first XC90s have a spacesaver in a cradle under the car, but the flat doesn't fit in it; instead you wrap the wheel in the bag supplied and put it in the boot. Cars fitted with the factory bodykit and twin exhausts don't have the cradle.
I've replaced spacesaver spares with a full sized one on several cars.
I went to one car with a flat that was still on the woman's drive. It wasn't a puncture, but was so badly worn it would no longer hold air. When I spotted that, I checked the other side, to find it too was worn through to the belts. When she asked if the tyre was repairable I declined to fit the spare as it was clear she would drive her leased company car until the other tyre failed. She
claimed to be an engineer....
My best stupid comment was a non-start. When I told him the cause, the owner insisted it couldn't be a flat battery "because this is a BMW!" It was a 10 year old 316 that looked like the last time the bonnet had been opened was for the PDI.