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In new symbology, when selecting size, width, offsets etc. in "map unit", the minimum value is either 0.00 or 0.01, because only 2 decimal places are allowed.
At 45° North latitude, 0.01 degree=786 meters, which renders symbology based on map unit useless on lat-long data at most scales.
It is impossible to chose for instance "0.0001" (about 8 meters) to represent a small road or a track.
The resolution should be at least 5 decimal places to support a minimum of "0.00001" (80cm), which makes sense for "street maps" (e.g. with "Open Street-Maps" data in lat-long): sometimes you find a path in very narrow streets, with buildings less than two meters away from each other.