As said, it's been discussed to death in here but I'll give you a simple short answer here. If you want more indepth information you could search for "blank plate" which will provide you with some decent reading.
The EGR is intended as an emission control to lower the temperatures achieved during combustion as higher temperatures cause nitrogen oxides to be created and these are harmful to the atmosphere.
By doing this, the engine's efficiency is reduced - power and fuel economy goes down a little. Blocking the EGR by installing the blanking plate reverses ALL of this.
In other words, you get hotter combustion, more power per stroke, better economy. It's only marginal - don't expect it to turn your ute into a formula 1 car.