The EGR recirculates exhaust gas into the intake to do 2 things:

1) Heat the air for better emissions
2) Burn off some of the excess waste gas by combustion

By blocking off the EGR, you may see lower intake air temperatures. This may hurt mileage, and emissions, but may improve horsepower. Depending on the design of the motor, and the specific output, this could be 1-2 hp (barely noticeable) or 15-20 hp.

Blocking off the EGR may also hurt "driveability" in that it may run leaner at times than normal, it may do some other things it technically shouldn't on cold starts, and/or on colder days. So although it can provide some power, if everything is right, and you're really needing it, it can also have some downfalls.

High horsepower, highly stressed applications, and older less efficient designs usually see the most benifit from blocking off the EGR, but there are exceptions.

What it would do on your specific application???? Ask someone with that application, that has done so.