I can understand the confusion.
When Big Dave instructs to weigh everything in the PMQ piece you read, he literally means to weigh everything. But he is talking in the context of a large pizza operation where dough making starts with a bag of flour weighing 50 pounds and even the relatively lightweight ingredients like yeast, salt, sugar, etc., can weigh several ounces and even pounds. To achieve uniform and consistent results in a professional pizza operation, all the ingredients, including the water, should be weighed. This is what most bakers do also since it is far easier to weigh a large amount of say, flour, rather than going into the 50-pound flour bag and scooping out flour using Pyrex cups or standard measuring cups, leveling off the flour, and keeping track of the number of cups scooped. Further, since a cup of flour will weigh differently when it is loose (or sifted) rather than solidly packed, using volume measurements is highly unreliable and inaccurate. The only way to achieve uniform and consistent results is to weigh everything, as Big Dave suggests.
Many of us at this forum follow the same practice as professional pizza makers and bakers, but on a smaller scale. Those of us who weigh ingredients usually weigh the heavier ingredients like flour and water using a scale, either a spring loaded scale or, more preferably, a digital scale, which is more accurate. Because most scales intended for home use are not accurate or precise enough to weigh very small amounts of relatively lightweight ingredients, like yeast, salt and sugar, we use conversion data to convert from weight to volume for those ingredients. It is possible to convert the weights of flour and water to volume also, and some of us do that for the benefit of those who do not have scales, but the conversions are not particularly accurate and can lead to problems in trying to practice the recipes in which such conversions are specified.
Since many recipes used by home cooks are specified in volume (e.g., a cup of flour or a cup of water), I can see how you were confused. But baking is different than cooking and the more prevalent practice among professional bakers, and many of us here on this forum, is to use weight rather than volume as much as possible.