[GMcL]

Until you need a spare, it's dead weight and dead space.
When you need a spare it is critical at the time.

Depends where you are what the priority is. Most manufacturers now offer breakdown recovery as part of annual servicing.

The UK appears to run 7 days/week service. Distress purchases are always going to get hammered in terms of price if you have some 235+ size tyres on 19+ rims.

I bought a space saver for my S60 in 2014. It takes up about 33% of available boot space and never seen the light of day since it was fitted.

Since I bought the Volvo in 2013 my wife and I have had four other cars between us each with a compressor and can of "stuff". None of those have seen the light of day either or needed replacement.

I've had a licence for 34 years. In that time I've had 3 punctures. I've also been towed off the motorway with a shattered windscreen - no spare provided - and also had two blown inter-cooler hoses, one FIAT, one Volvo.

Back to manageable risk.