What does a EGR Valve do

What does a EGR Valve do? If it is a bad valve, what are the symptoms and is it okay to drive?

Thanks

First off what year and size of engine do you have??? I wil try to help
anyways egr stands for exhaust gas recirculating and what it does it
alows the engine to reburn unburned exhaust gasses under certain
conditions. Now there are a few different ways to fail, if stuck open vehicle generaly runs very rough at idle or will not idle at all unless you assist it with the accelorator pedal and engine is execevilly rich and may see black smoke from tailpipe and not recomended to drive too much
could plug catalytic coverter and could kill your o2 sensors and also hard
on the engine washing oil off cylinder walls . Now if stuck closed you may not eaven notice any driveability differences at al but you may notice a sligh higher fuel consumption but basically engine lamp will be on
and will fail any emission test and required to be functional by law and should be repaired . If engine lamp is always on you wont know when you have another problem until it's too late and creates more damage.
My advice would be repair the problem. I have 30 years experience repairing Chrysler Dodge Plymouth line up.