Don't know exactly ... descriptions are relative in free space. Water and general diesel quality in the USA is claimed as a significant killer of HPFP systems (per my 535d that got a $14k fuel system.)
I don't care about much of what they describe, since I run additives periodically to help with various factors they point out. It's the water issue that is the single killer. In the description below they seem to say that water separation is at the storage tank ... THAT I'd like to know more about ...
Unfortunately it seems that Shell began a "test market" activity ... in 2014 in the Seattle area ... and I see no new updates. That's not encouraging.
--- from Shell ---
With continuous use, the exclusive Shell Diesel FiT formula provides the following benefits:
Carbon Deposit Build-Up: Fuel injectors deposits can reduce combustion efficiency, which can increase fuel consumption. The exclusive Shell Diesel FiT formula protects against deposit build-up to help maintain proper injector fuel flow and spray pattern and provide designed power and performance.
Anti-Corrosion: Use of diesel meeting minimum government quality standards can result in corrosion of vital engine parts such as the fuel pump. Shell Diesel FiT contains enhanced corrosion inhibitors to help prevent fuel system corrosion to protect your investment.
Anti-Wear: Shell Diesel FiT is formulated to help provide additional anti-wear protection for your diesel engine exceeding minimum government quality standards to help protect your investment.
Anti-Gelling: In severe winter conditions, diesel meeting minimum government standards can “gel” resulting in the inability to start the vehicle or reduce diesel engine performance. During winter, in select cold weather markets, Shell Diesel FiT contains anti-gelling agents for enhanced cold weather performance. Look for the "Special winterized anti-gel formula" label on the dispenser.
Water Management: Shell Diesel FiT is specially formulated to separate water from fuel and assist in water removal from fuel storage tanks to help provide consumers with dry fuel.
Heavy-Duty Truck Fuel Economy & CO2 Savings: Based on extensive tests, Shell Diesel FiT achieved a 1.3% mpg saving for heavy-duty trucks in long-haul service and an impressive 4.8% mpg saving for heavy duty trucks in more severe stop and go city conditions, compared to regular diesel meeting only minimum government standards.