I did this with a shear top brass measure set at 90 grains.
Comparison of powder by weight when measure is tapped and untapped before leveling the measure.
First, the 10 that were poured and sheared without tapping the measure
93.5
94.1
93.2
92.5
92.8
93.6
94.0
92.8
93.5
92.2
93.2 Average Weight
.63 Standard Deviation
1.9 Extreme Spread
Next, the ten that were tapped and then sheared
94.3
94.2
93.5
93.9
93.8
94.1
94.1
94.0
94.1
94.3
94.0 Average Weight
.25 Standard Deviation
.8 Extreme Spread
All can decide for themselves how important the differences are. I don't post these little experiments to make a point about anything. I do it for my own entertainment. I did the comparison of tapping (settling) the powder charge because I wanted to prove to myself that tapping the measure and settling the powder would be LESS accurate than pouring and shearing it off without tapping. As you can see, I ended up discarding my opinion.
One might expect that these results have converted me to tapping my measure. NOT! Too much trouble. Furthermore, it would take probably 50 shots fired from a vice to determine the difference if it could even be measured.