When I was in the insurance industry they were the devil.
We could deny coverage to an insured if they had tinted tail lights that may have been a factor in the accident.
Also, tinted tails were often connected to insurance scammers. People would get an older car, deeply tint the tail lights, then purposely pull out in front of you at night causing you to rear-end them. They would then attempt to collect damages from the accident.
Some of them were slick enough that when the auto appraiser went out to see the damaged vehicle, they would remove the tinted lights and replace them with normal ones. This was pretty obvious when the whole rear of the vehicle was smashed in but the tail lights were untouched.
Dash cameras are invaluable in these situations.