Actually ... those 'Temporary' spare tires (I call these "Pretend" spares) found in many newer vehicles are considerably smaller in diameter than most regular "full size" tires
So installation creates a huge differential in roll-out between the rear tires when installed on rear drive vehicles and can lead to axle/differential issues if run for extended periods.
That said - I still carry one in my 'vert as the spare
The trunk space is constricted enough in a 'vert and every little bit helps.
I've only used it once, and luckily it was for an issue with a front tire.
I only used it to get the vehicle off a major road and to a service center where I could get the defective tire replaced right away. (they didn't have the size or brand I was running, so I just bought a another tire close to the size and had them mount it on my rim - replaced that as soon as I got home and still have that one odd sized nearly brand new tire in the shop
I found the 'Pretend' spare I have at a 'Pick-N-Pull' place on one of the sale days - think I paid @$10 for it
I just looked though the trunks of a bunch on GM cars until I found a nice, good sized one with 4.75-on-5 pattern ...