Composite stocks provide superior durability and accuracy as well as a defense against the elements that can cause wood stocks to warp and swell. Browning composite stocks are made from the toughest materials; many of them, such as the stock on the x-bolt are made from glass fiber reinforced polymers.
One of the keys to accuracy is consistency. Wood is a porous material, that while strong, is prone to swell and deform with exposure to humidity and heat. This can cause the stock to vary its pressure and contact with the barrel, thereby changing the point of impact on a zeroed rifle. Not all composite stocks are completely impervious to absorbing moisture and other shape deforming factors, but they tend to be more resistant than wood.
While it is hard to beat the classic looks of walnut and blued steel, synthetic stocks have come a long way toward being aesthetically pleasing. Virtually every camouflage finish in the Browning line is applied to a composite stock. Many models are available with a carbon fiber finish as well. Perhaps the greatest advantage that synthetic stocks provide is variety.