Ok: If you understand what bogie and I posted , that a lifter can hold pressure for a long time with valve spring pressure on it!!! And you pump them up and install them they can hold this pressure during your dry assembly! So when priming the engine they are already filled and holding the valves at max because you filled them already! Now when you first start the engine and quickly bring it to 2500 rpm a few lifters might hold valves open (till the lifters metering system bleeds some oil) causing loss of compression delaying start up and as the engine cranks your break in lube is being rubbed off your lobes and lifters you then can cause damage to the cam and lifters! But if your lifters are installed not pumped up and you do your engine prime with valves set at initial adjustment, as you turn engine over by hand while priming the gallys, the lifters will fill to running position because they have valve spring pressure being supplied to them! You hit the key and your engine has compression from the get go! No delay no rough running till they bleed off! If you have very close tolerances and the prepumped up lifters happen to hold the valves open a hair too much you may have slight contact and bend or damage your valve train!
100,000 people may never see a damage caused by pumping up their lifter before installation but if you are the one in the 100,000 that does
you will wish you read and followed directions
If you don't understand Im sorry I tried to type it as simple as I could Maybe someone can explain it better then I. I understand it and know what I am trying to tell you so it looks good to me