It used to be worse. Lots of cars today use a coil-over-strut design that captures the spring. There's still a lot of energy, but it's much easier to manage safely, by the time the nut at the top runs out of threads there's generally little to no force left in the spring.
Way back (like... 30 years ago) when I was working on my Mustang, the spring was separate from the strut. You had to drop the control arm enough to unload it and remove it, and there wasn't anything to contain it. I always tied it with a chain or a seat belt, and tried to not be directly in front of it during the unloading process. I knew a kid who got hit in the chest by a spring popping out; he did not make it. Removing it or installing a new one were both quite dangerous for the careless.
The back springs in many cars are still separate from the shock absorber and it is those back springs which often fail. I have replaced them on several cars and can only conclude that the job can be done safely as long as you use a pair of reasonable-quality spring compressors - two of them, one on each side of the coil so that it can not pop out. These are used both during the unloading of the old spring as well as when installing the new ones.
> by the time the nut at the top [of a McPherson strut] runs out of threads there's generally little to no force left in the spring
This might be true on heavily lowered cars, but cars at stock ride height [with stock springs IOW] this is not my experience at all. I sure wouldn't risk my life or limb on it and spring compressors are quite cheap compared to an ER co-pay.
Way back (like... 30 years ago) when I was working on my Mustang, the spring was separate from the strut. You had to drop the control arm enough to unload it and remove it, and there wasn't anything to contain it. I always tied it with a chain or a seat belt, and tried to not be directly in front of it during the unloading process. I knew a kid who got hit in the chest by a spring popping out; he did not make it. Removing it or installing a new one were both quite dangerous for the careless.