I don't aggre with broad statements like that. The fuel here is so bad that when I didn't use an aftermarket additive I had to rebuild injector pumps every 30,000 kilometers or so. With an aftermarket additive in every tank, I now have one diesel pickup that had had 4 rebuilds in 2 years with not a single problem in the last 480,000 kilometers with the additive. Another truck that had several rebuilds now has more than 200,000 km without a rebuild. My 95 diesel 4Runner had a rebuild at 110,000 before I started using the additive. It now has 300,000 km with no more repairs. My 99 Turbo-diesel 4Runner has 72,000 km on it, using the additive since it had 16,000. No repairs.
This additive elimiates black smoke, gets better mileage, better cold weather starts,etc.