The standard blades are symmetrical in profile to give the same lift whether upright or inverted. For the scale flyers there are A symmetrical blades to give more lift at lower head speeds, and those guys aren't worried about inverted. With Flybarred helis you have the weights in the flybar which add stability to the heli. On Flybarless helis, to give more stability, the main blades are weighted in the tips to give the same effect.
As for the construction, as mentioned already, the stiffness will reduce the energy loss and give a crisper feel to the controls. The disadvantage in a crash, would be the stiffness. A lot of energy would be transfered to other parts of the head, causing more damage. When learning to hover a set of Fibre glass blades will do the job, or even a good set of Align wood blades to reduce the risks of head damage. But nothing beats the carbon blade for performance.