You are right in that EGR is exhaust gas recirculation.
Basically taking the "intert" exhaust gas, and returing it to the intake to do various things.
First and foremost, being an intert gas, it slows down the reaction of combustion- which does two things- the primary goal to reduce NOx. But it also reduces power, since peak pressures are not as high.
Quite contrary to what I just wrote, if done properly (not likely on the Geo), EGR can help fuel economy. Since the gas replaces the air, one can run with higher manifold pressures- more throtte- and less pumping losses. In addition to that, EGR can allow the engine to run more advanced spark, since it's much less likely to detonate. SO, IF DONE CORRECTLY- all of that can add up to more gains than the losses in combustion efficiency.
Anyway, you should leave it on. Better for the environment.
Eric