Insurance often doesn’t give a damn how fast the person in front slammed on their brakes. You rear-end, it’s your fault.
I know someone who was rear-ended at a stoplight when the guy stopped behind her was rear-ended and pushed into her. BOTH other drivers were deemed at fault – even though stopped, they ruled that the middle driver should have left more space in case they suddenly moved forward. She was NOT held at fault because she had done exactly that.
Moral of the story: always leave extra distance regardless of speed – you and your wallet will hurt less.
Sometimes the financial motivation is the only one certain idiots will pay attention to.