The issue is that for a lot of ingredients -- flour notably among them -- you can't measure accurately by volume. If you're looking for reproducibility, you have to measure by weight.

And once you start measuring some things by weight, you quickly realize that most things are easier to measure out by weight than volume (particularly sticky ingredients like honey), so you start wanting to measure everything that isn't a tiny amount by weight.

I convert all of the recipes I collect to gram measurements for this reason.