Is the EGR valve necissary?

[matchstick321]

Howdy, I'm new here so I'm not sure how to do this but here it goes.
I have a 1979 chevrolet k20 pick-up that my brother-in-law gave me.
It has a 350 engine with 4 barrel quadrajet carburetor and I got to looking in my owner shop manual and came across a page about the EGR valve I took a look at my engine to find that I did not have one...
I found that it had a plate bolted in where it where the valve was soposed to be.
I was wondering what exactly it did, if it uped the proformance of the engine or maybe even the fuel mileage, and if it would screw up my engine any not to have it.