The EGR adds back burned gasses to the intake charge, thereby taking up some of the space that a fresh air/fuel mixture would otherwise fill. In this way, it helps extend fuel mileage. The burned gasses obviously can't be burned again, so in this way it helps control the flame front (burn rate) of the igniting air/fuel charge. This helps control pinging.

The EGR is a good thing to have operating correctly, unless you are a looking for all-out horsepower and performance with no requirement for fuel economy or emissions control.

Mike in AR