I finally got my free resonator from Traxxas yesterday. Being new to this what are the benefits of it if any. I did take notice that the exhaust port is much larger and I know it will make it louder. Will it make it run richer or leaner?

Generally speaking it should give you better exhaust flow which will allow more air to be pumped through which you guessed it, will make it run leaner. I'd richen things up a little before running it.