Printing speed and Extruder speed

If I lower printing speed to -50%, is the whole printing process that is lowered or only printing mm/s ?
Shall I reduce even extruder speed to -50% to have a whole printing process reduced by 50% ?


I’ve tested this last week and turns out the extruder speed is actually the flow rate, therefore it only need to be adjusted when you are printing something like foaming material (PLA-LW for example) or something needs to be higher density.