[derbOac]

I measure by mass when I bake, but I've always had the same questions as you (about humidity, for example). That was always the answer I got when discussing volume versus mass measurements — that volume can change due to all sorts of things — but it always seemed to me that mass could change for the same reasons.

I eventually decided mass measurements are most useful when the amount you need in mass is fairly small relative to the volume of the particles of the thing you're measuring. Measuring a small volume of nuts can be tricky, for example, because the nuts are different sizes and shapes, but mass is fairly consistent.

Measurement with baking in general is conducive to replicability assuming the same conditions are met. That is, that you're in the same bakery, with the same oven, same flour, and so forth. It becomes less reliable as you start changing variables.

This is pretty obvious even with flour: two bread flours can absorb really different amounts of water, so you almost have to be aware of texture and so forth. What you want to achieve in a recipe is a certain outcome, in dough characteristics and final loaf. How you get there can be informed by a bunch of things but is never guaranteed unless everything is the same every time.

[PaulDavisThe1st]

Volume changes easily with differences in your manual technique (and to some degree and for some things, storage conditions).

Mass will only change based on things not related to your in-the-moment technique (e.g. humidity).