Winchester69 has it right!
Even if you weigh your powder precisely on one day, on another day it MAY be different due to humidity changes.
Whether it's weighed or measured, a .1gr+/- is not going to show any significant change in velocity, but due to the same humidity change, it may show a significant vertical dispersion on target due to changes in combustion.
This is a little known fact by many loaders, that's why in benchrest they tune their loads on the day, not the week before!
I always use the same setting on my measure, whether it corresponds with the initial weight setting or not! I have had differing weights of 1.5gr's on any given day, and it doesn't seem to affect accuracy or velocity a great deal. Rarely does this pose a problem once a 'node' is found, a good 'node' will run 1gr+/- without affecting anything drastically.