1) The higher the octane number on petrol, the more refined the fuel. The better the performance and coincidentally fuel efficiency. 95, 93 are the norm. The higher the octane, the cleaner you likely to see on your tailpipe.
2) With diesel, the refinement is shown by PPM which equates to Sulphur in the diesel. Parts Per Million (PPM). There is 500ppm, 50ppm and 10ppm. The lower the PPM, the better refined the diesel. This also equates to better engine performance, efficiency.
3) "Bucket" diesel and petrol has foreign items which can easily enter and damage the injection system of your engine. These can include dirt, liquids. Some people that sell these buckets add paraffin and even water. If you fill your car up with this and it has a failure, the dealers technicians will find out and you might lose your warranty.
4) In Mzansi, we get charged Emissions Tax and yet there is no investment on cleaner fuels and EV support. The emissions tax is calculated on the Co2 emissions that come out of the exhaust. The cleaner the engine, the lower the emissions. Billions in Rands are raised when new cars are purchased and yet the fuel quality we have in Mzansi doesn't allow car manufacturers to bring their cleanest engines.