The purpose of the powder baffle is to keep a constant "head" (to use the engineering term) on the powder that's flowing into the metering cavity. If the powder measure is nearly full, without a baffle, the powder will exert more pressure at the bottom of the measure, thus packing more powder into the metering cavity. When the powder level is low, the opposite happens and less powder is packed in. Sorta like the high school experiment to demonstrate that pressure increases with depth, where you punch holes vertically in a can and observe that the water flows out of the lower holes faster than it does out of the upper holes. In a powder measure, the difference is probably very small, but, in theory at least, metering accuracy should be constant as the powder level goes down if you're using a powder baffle.