No matter how hard you try, there will always be water in the fuel tanks that builds up due condensation. Eventually the water precipitates to the bottom of the tank and the boundary between the fuel and the water is a excellent area for the formation of biological growth. It appears as a black smelly slime and it will plug fuel lines, foul fuel system pumps, and cause significant corrosion to the fuel tank structure as most tanks do not have fuel bladders.
I don't know about any effects on fuel tank sealant.
So Biobar or a similar formula is added to the fuel to do away with these growths in their infancy. Many maintenance programs include adding Biobar to the fuel tanks on a regular basis.