Despite the fact that even good filament is often not perfectly round different filaments need different flow rates due to shrinkage and other tolerances.
And with a good printer you will see deviations of the cross section of a filament string.
Back in the days I measured the filament with an outside micrometer to get the same settings and flow for the same filament type from the same vendor.
And there are some settings in the slicer where you want to have control over the flow/EM.
So it is not really off-topic.