Plus there is Speed VS RPM vs Manifold Pressure
There's a whole bunch of technical stuff that the pilot of an aircraft has to consider which impacts the tactical operation of his craft (not surprisingly). For planes with variable pitch propellors the pitch of the props greatly affected the range that the plane could fly on a mission. I read an account of a combat mission flown by civilian test pilot Charles Linbergh in WW2 where, flying some model of P-38 against the Japanese he returned from the mission with "half a tank of gas" while all the USAAF pilots were "sucking fumes" when they landed. IIRC it had something to do with propellor pitch and RPMs. He also showed the Marines that it was possible to take off in an F4U with 4000 lbs of bombs attached (presumably a fairly short range mission). Wish I could remember the name of that book (also had a story about the Boston baseball player Ted Williams in an F9F getting shot up over Korea and subsequently ditching).
The propeller pitch angle is much like the gears in a car. Except that instead of discrete number of gears you can set it continuously.
So the "right" pitch angle will be different depending on what you need. If you want to cruise (read fuel economy) at certain altitude in certain weather conditions (humidity, air pressure, etc) you will have a certain "perfect" propeller pitch angle.
If you want maximum acceleration at the same conditions you will need different "perfect" propeller pitch angle.
And so forth.
If I recall correctly, FW 190 had automatic pitch control, and I am pretty sure that near the end of the war all modern fighter had it.
Of course, just like in real cars, an experienced pilot using manual pitch can outperform a less experienced one or one using automatic pitch control. The price is that constantly fiddling with it will lower your situational awareness.
We, the capable, led by the clueless, do the impossible for the good of the ungrateful. And we did so much , with so little, in so small time, that we are now qualified to make anything from nothing.
Konstantin Josef Jireček