It is lighter than a full spare wheel and takes up less space. This makes even more sense, if one considers that, statistically seen, the spare wheel is not even used once in ten years. The introduction was a good idea, even if it has now lost a lot of its meaning ...
The question - emergency- or full spare wheel - must be answered positively, in spite of the fact that there are a few vehicles with differing tyre sizes for the front and the rear. However, for the most part, the emergency spare wheel has concrete advantages. Assuming that the average driver clocks up less than 15.000 Km per year. With the (mostly used) front-wheel drive vehicles, the front tyres are due for a change after 4-5 years. There is a very real danger of the spare tyre landing on the front axle together with a brand new tyre. Not only is the spare a lot older, it also contains less softener. Even if the profile is the same, the carcass and the rubber mixture have generally been developed further. If the front axle has as little as ten percent difference in grip on wet roads, it can be very dangerous. A long holiday journey offers the best additional argument against the emergency spare wheel. In the event of tyre damage, one must have at least one new tyre fitted. This argument is also not valid, after all, who would undertake the risk of a long journey with a defective spare tyre? This means, even with a spare wheel, a trip to the tyre dealer while you're on holiday anyway.
If the danger of a flat tyre is that unlikely, and one can't solve the problem with a compressor and/or sealing agent, (aerosol spray) then the emergency spare is the best alternative. However, in that case, a little bit of work is necessary, because the emergency spare should always be used on the rear axle.