I look at it like filtration (or insurance). CAN I run a tractor (or any other diesel) w/o fuel filters? Sure, assuming clean tank/clean fuel/no possibility of water/condensation/rust/dust/or any other contamination getting in between oil refinery and my injector or fuel pump. Would I do it? Hell no, downsides outweigh the costs of prevention. I might be able to control some of the variables, but not ALL of them. Biocide is relatively cheap/a little goes a long way, and like water separators & filters, it gives me piece of mind. Yeah, water is necessary for algae/yeast/ etc. to grow. Won't happen in pure diesel oil (maybe someone with more biodiesel/farming/moonshining experience can speak to vegetable oil critters), but I never KNOW how pure I'm getting until after the fact. All I can do is assume based on prior experience. I might feel different if I operate in the Sahara, but I run in high humidity areas & don't know the status of tanks at the gas station, or whether biodiesel (or moisture absorbing ethanol gas) accidently got mixed in by an inattentive tanker driver, or how often they stick the tanks & if they do, how they remediate if they find water. Too many variables to take chances (in my opinion).
