Advancing cam 2 degrees

Ive read a couple of old posts that said to advance cam 2 degrees in stock 318. Technically how does this increase performance. I am looking for MPG,bottom end and midrange from my 75 stock 318 . It is a 4spd o/d 66 Dart with a 3.55 sure grip. I wiil be converting from 2 barrel to T-quad and performer manifold.