[Longhorn Man]

Your crank case is filled with misted oil particles, fuel vapors, and residude from the conbustion that gets by your rings. All this is normal. When all this mixes together, along with water vapor from the humidity in the air, it becomes acidic, and contaminates your oil.
The PCV sucks all that crap out of the air that is trapped in the crankcase, and feeds it into the incoming air/fuel that is headed to the comustion chaimber for burning.
For simplicity, we'll compair the crankcase with your kitchen after you burned your dinner real good. I mean REAL good, thick smoke, hardly see across the room, let alone inhale.
1. You can open one window, and that'll let some air out.
2. Or you can open 2 windows... that's be better.
3. Or, you can open both windows, and place a window fan in one aimed out, to suck all the smoke out, while clean, fresh air comes in the other window on the other side of the room.

#1 is your engine with one breather.
#2 is your engine with 2 breathers.
#3 is one breather, and a PCV valve.

While this IS a polution control device, (and reqired federally in all 69 and later trucks, 64 and later in cars) it is one that has no performance killing drawbacks, and HELPS your engine last longer and run cleaner. And by cleaner, i don't mean smog, I mean crap in the oil, getting ground into the bearings and cylinder walls, causing poor oil pressure and less performance.

The way the factory did it on these trucks, was an oil fill, a PCV, ans a fresh air tube that was plumbed into a steel collar that went under the air filter. This is better than just a breather, this way, the fresh air being sucked into the engine, has been filtered by the large airfilter that is on top of the carb.

Installling 2 doesn't do anything good. If you have 2 on the same valve cover, with the fresh air inlet (breather or tube to the air filter) then it may do more than just one. If you install one PCV valve on each valve cover, with no vent, you can suck a gasket into the engine. Usually the intake end gaskets. If you do a PCV on each cover, and one vent, then the air inside that is supposed to flow from one side to the other gets disrupted. If you seal the engine off, no PCV, no vent, no road draft tube (pre PCV system) then you will end up building up positive pressure inside the crank case and spitting gaskets out.

Some remove them for aesthetic reasons, personally, I don't see them as being all that ugly. you can get aluminum ones from places like Jeggs or summit, and then steel braided hose if it pleases your eyes a little more, but in my personal opinion, it is a must have for anything but an all out show truck that rides in a trailer to get to the show.