In England they seem to teach that it's OK to tin two wires and just melt them together. I've seen that done a number of times on different UK car shows, by allegedly professional mechanics. The reputation for unreliable electrics in British cars is not just the fault of Lucas.

 

One thing becomes important and that is the application and the voltage. What is quite OK for a $100 stereo speaker system is not at all OK for 120 volt/ 15 amp service mains power in your house, and even wiring up speakers in the car has a different set of requirements. And none of those methods will be OK to use in the car's engine compartment.

 

Whenever you come across a really big cable (25mm^2 and above) where a low resistance connection really matters, it will always be crimped.

When I started out on my career voyage in the UK, solder-pot terminals were allowed, these are no longer allowed and must be crimped.