Cartridge case volumes and bullet weights are not identical to one another, rather they fall within certain tolerances. Match and varmint bullets usually have tighter weight tolerances than hunting bullets, and premium brass like Lapua or Nosler usually have tighter volume tolerances than bulk brass, but they still fall within certain tolerances and are not identical to one another. This is another reason why its usually pointless to worry about keeping powder charge variances to a tenth of a grain in rifle cartridges.
Having said that, I think its a good practice to keep the tolerances that you can control at the loading bench to a minimum and weighing powder charges is a good example of that, keeping brass trimmed to the correct length is another, as is annealing case necks, both of which affect the bullet pull weight, which if not uniform results in poor accuracy. I bought a scale that measures to 2 decimal points so that I can be sure that the tenth of a grain reading I get is correct. The more accurate the scale is though, the more challenging it can be to use due to its greater sensitivity.
I weigh and never throw charges for maximum loads for either rifle or handgun loads. When I do use a powder measure, I only use ball powder or short extruded powder, never long extruded or flake powders. Long extruded powder particles get cut up by the powder measure's drum which sets up vibration within the hopper, settling the powder and affecting the volume of the subsequent thrown charge, while flake powder hangs up due to its light weight and large surface area. When I want to throw charges with long extruded or flake powders I use Lee Spoons which can be used with surprising consistency once you establish a good procedure with them. The results obtained with a powder measure are affected by the technique of the user more so than any other tool on the loading bench. The speed at which you roll the drum should be consistent, and you should avoid banging the drum on the stop at either end of the rotation.
I weigh every fifth thrown charge to ensure the consistency of the powder measure, which can be affected by the height of the powder in the powder measure's hopper. I think its a good practice to keep the powder hopper topped up, regardless of whether a baffle is used or not. I also consider it a good practice to check the consistency of the scale with a set of check weights, if my scale gets bumped, I'll put check weights on the pan, equal to the charge weight, to ensure the scale is still reading true. If it doesn't read true, I re-zero it.
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