Very rare to be honest. It's just good having a space saver as a back up to limp home and then change for a full size wheel until the tyre gets fixed. It was just this guy was of the opinion he was right and everyone else is wrong. As I say he has a rep for being a bit of a BS'er at work.
Can you imagine not even having a space saver, a can of tyre foam and a blow out in the middle of nowhere and no phone signal. Time for a long walk.
That was the situation with my TT, which had 19's. I got an 18" space-saver from a Golf GTI and managed to find enough space under the boot floor. It's a recognised solution with TT's and, as above, the 18 is fine as a spare with the 19's.
Modern tyres do seem to be pretty puncture resistant, though. (Touches wood!)