Cooking is jazz. Baking is chemistry. A tablespoon here and a pinch there is fine for a stew and disastrous for a soufflé.
The volume-vs-weight problem
A cup of flour can weigh anywhere from 120 g to 155 g depending on how tightly it is packed. That is a 30% variance. Bake a cake with an extra 30% flour and it will be dense, dry, and inedible. Bake it with 30% less and it will collapse.
Grams do not vary. A recipe that says 250 g flour is a recipe you can reproduce.
What to weigh, what to measure
Weigh: flour, sugar, butter, chocolate, salt. Measure: liquid volumes (water, milk, oil), extracts, spices under 5 g. A digital kitchen scale with 0.1 g precision on the low range is the single best investment a home baker can make.
Temperature also matters
Water temperature affects yeast activity. Room temperature affects butter behavior in creaming. Refrigerated eggs behave differently than room-temperature eggs when folded. Precision extends beyond weight.