Hang on a minute, i'm sure i'm not going mad here. A pump controller generally does two things..........
Allows you to set the pressure before dead end shut off.........
And allows to to set the flow...3,4,5, or 45,45,47,48 etc.. depending upon what type of pump controller you have.
Setting the pressure before cut off generally requires going into some mode or other and setting it (calibration), setting the flow requires no more than adjusting the dial, or digital number on the display.
Yes of course you can adjust your flow further using a tap, in practice this means restricting the flow (as a tap can't make it go any faster than the controller is set at). If any of you guys are slowing your flow down with a tap and you have a pump controller then i guess you're missing the point of the equiptment you have.
Of course if you have one of these ...........'Brodex Systems that are set up to bypass the pressure switch and so aren't suitable for use with a flow controller'. Then your pump will just run full blast and you won't need a digital dial like the brodex one in the photograph. Bit of a conundrum i know !! I'd guess this type system aside from having a useless dial would also need a bypass for when you switched your tap off. All sounds like rubbish to me to be honest.