meters can not measure the impedance and capacitance of the antenna system. They only read fwd and reflected power.
the mfj can see much more.
I have personally seen changes in performance by altering coax length. both in the feed line and jumpers.
Once again real life findings.

What the average t bag doesnt understand ( resident who ) is each foot of coax has capacitance to it. Jumper length matters due to this!!! it can does and will affect the input or output tuning of the amplifier.

if you dont use 1/2 wavelength intervals with VF factored in on your antenna, you may as well try sucking a milkshake through 12 in of big straw and then 2 in of a coctail straw. its not optimal. But you dont have to believe me. The ones who dont can go on being the biggest duck they can be.