As you read in the answer to question 2, biofilms can build up on boat bottoms and create friction that reduces the boats' speed. The microbes that make up biofilms also may produce acidic chemicals as by-products of their daily metabolic (basically, eating and breathing) processes. These chemicals could corrode the boat surfaces. The same is true of biofilms that form on your teeth. The acidic chemicals the microbes make gradually corrode tooth enamel, causing cavities. Biofilms can also build up in pipes, clogging drains.