How does Primetower in 3D Printing work?

[bluefiree12]

Hi,
i have a question regarding the primetower function in luban 3D Printing. My understanding was, that every time the nozzle needs to switch, the toolhead will go to the primetower and do some extrusion with the new nozzle there before coming back to the actual print. But this seems not to be the case. The nozzles are often switched but not allways primed on the primetower. Is there a special setting for this or am i getting this all the way wrong?