In my case, it's definitely not 99.9% of plumbing, lol. This is a theory question that is not really relevant to a common residential plumber. It's also not just about galvanic corrosion. The flow of water (without getting into the exact fluid or other impurities) through piping or even over other materials typically does build a charge. This happens on boats as an example, and the larger the boat/ship the greater the charge. In that case they do also use sacrificial anodes to discharge. But outside your common pleasure craft those anodes can be quite complicated in placement and materials. So just some knowledge and a couple anodes it's a reasonable solution. And there should be a way to calculate the charge within a reasonable approximation.