Think of fuel additives as dietary supplements. If your body is deficient in something, like iron, you’d take an iron pill and get better. Fuel additives work the same way for machines and tanks, because just like you, your tank or machine has systems and needs too. Running these tanks or machines can come with any number of maintenance problems, from sludge build-up to thermal degradation to fuel gelling, and if you wait around long enough those problems will shut down your machine/tank and cost you a wallet and a half to fix. Now if on the other hand you had employed the regular use of a fuel additive, one that would slow down/prevent sludge build-up, fuel gelling, and thermal degradation, you could have avoided this whole problem.
And not only that, but using these additives makes your machine/tank run smoother, too. On the road to machine/tank ruination through neglect, the machine/tank starts slowing down and running less efficiently. By using additives, you keep your machine or tank healthy and clean which in turn boosts performance and saves you a nice chunk of change on fuel costs.