EGR Question

[87Cutlass Ciera]

What kind of issues would a non-working/not properly functioning EGR valve cause? I was just wondering cause I've been noticing a slight hesitation with the Cutlass C. When I was putting the car back together in May/June I checked the EGR valve on the new motor and the diaphram moved and it sucked/blew air out of the vaccum line. I know that if you want to test it you just take the line off and plug it, but I can't remember what I'm testing. I remember the guy who inspected the car, last year when I had the missing problem, he unplugged it and I drove it with no differences (because it was my coil packs.) So yeah what issues are involved around a not properly working EGR valve?

CRC
Oh, haha 1988 2.5L (Fiero Transplant)