3D printer nozzles - Are they actually what they are? 

Good videos man! Nice and technical with actual information....useful stuff!

It can go either way on weather to tune the flow rate by either adjusting rotational distance, nozzle size or flow rate. Ideally you should have the rotational distance of the extruder down to where 1mm of requested filament equals 1mm of actual filament but since there are deviations in the diameter on filament its worth filtering then out by using a best average for the flow rate. If both of those seem perfect but the walls are not sticking to each other or overlapping too much you can adjust the nozzle diameter and the slicer SHOULD space out the lines accordingly but this part in particular depends greatly on the slicer used. Lastly its possible to adjust the extruder wall thickness to a bigger width than the nozzle and thru the magic of die swell as the material comes out of the nozzle it will actually function as a nozzle of a bigger size. There is a channel where someone extruded 2mm wide layers with a 0.4mn nozzle but the speed had to be really slow so the heater could keep up.

In what field/ work do you do , that you have access to such beautiful machines?

Announce the diameter doesn't actually have any effect on printing parameters directly. I can use a 0.4 mm nozzle and extrude out to 0.7 mm wide by setting it in my slicer.