I think the argument about masturbation (or sex) just focuses on the timing in relation to PE. The one theory being, that if/when you are going to masturbate or have sex, it should be several hours after completing your PE routine.
I just find that for me, it does not effect me at all to masturbate directly after a long PE session and in fact it helps.
Now some guys try to masturbate before PE to try and control erections during PE. I have never tried that and wouldn’t recommend it as a long term solution. Eventually, your body should become used to the fact that PE is an exercise regime and the erection during PE problem should begin to diminish, thus eliminating the need to masturbate before hand.