I've heard that for a lot of cooking it doesn't matter, and for some it matters a lot.
A large category where it matters a lot (I've heard) is baking. If you're making a soup or a sauce or some mashed potatoes, most of your changes are predictable and linear -- less salt means less salty. Less butter means less buttery. But when you bake things interact in sharp ways, and the ingredients interact with each other in more interesting ways. Maybe "less predictably" with certain priors -- not in a strong sense (it's chemistry). But in a weaker sense, "why didn't it rise" isn't answerable by "didn't add enough X" for any fixed X, and in most recipes 2X won't mean "twice as much rising".
A large category where it matters a lot (I've heard) is baking. If you're making a soup or a sauce or some mashed potatoes, most of your changes are predictable and linear -- less salt means less salty. Less butter means less buttery. But when you bake things interact in sharp ways, and the ingredients interact with each other in more interesting ways. Maybe "less predictably" with certain priors -- not in a strong sense (it's chemistry). But in a weaker sense, "why didn't it rise" isn't answerable by "didn't add enough X" for any fixed X, and in most recipes 2X won't mean "twice as much rising".