Since the title was “Bigger picture,” here’s a different answer. If you are using hand tools instead of machining wood, then keep in mind that many of the techniques will make the exact thickness of the wood not matter. So, if you can get the thickness uniform enough to be visually acceptable, the rest often will not matter. For example, suppose you are making a drawer and the sides are not thicknessed exactly the same. Since you layout dovetails from the actually thickness of the material being worked, and since you label the corners as you cut the dovetails, you will get perfect corners even though the thicknesses are not the same. You just have to keep track of things (label the joints) and not make assumptions (like setting a gauge once and assuming it will work for every joint). Another example would be laminating a top. You have to plane it flat when it is glued up anyway, so this thickness is not important. How about the legs of a chair, if they are close enough to be visually acceptable? Again, it will not matter if you fit your mortise and tenons to what is actually in hand piece by piece. Is that a waste of time? I don’t think so- It is just being precise. You’d do it with machined wood too.

I think what you are asking is a good skill to have, and we do have to get things to the same thickness to a reasonable degree, but at some point if you are not using machines, leave the machines behind and take advantage of the hand joinery techniques. This also means if someone gives you plans for a piece made from 1″ material and you have 7/8 material, you’ll know exactly what to do- Key lengths will matter, and the setbacks from thicknesses (that come from gauges or transfers by knife) will just take care of themselves.