I was at Jim's shop last year and he was able to show me the differences in the type of carbons that he uses for his bows. Essentially, Jim uses three different types of carbon lams, one designed for tension (front), one designed for compression (belly), and one designed for torsional stability (the XTL lamination). Jim then proceeded to show me the difference in the torsional stability in the XTL lam compared to a regular wood lam. There was a noticeable difference between the two, the carbon used for the XTL had much more torsional resistance compared to a wood lam.
Long story short, if you have a perfect release and do not have to worry about the torsional stability of the limb then you probably do not need it; however, if your release is not perfect and you want something more forgiving you might consider it.
Jim has put a lot of thought and engineering into his carbon laminations in order to provide the best make up possible. It sure looked to me like the XTL lam had been well thought out and designed.