Wiggy,
I presume that you are talking about how you load the aircraft. In this case they are talking about ALTERNATE FORWARD CG, this means that the forward CG limit is moved aft and the performance is based on this position for the reasons mentioned by MFS and Blackmail.
In your case, i dont see how you can benefit from moving cargo aft unless you have a seperate CG envelope and associated performance.
On the E170, moving the Forward CG limit from 7%-16% can increase limiting takeoff weights by around 3-400 kgs.
Mutt