If the hand guards do not touch the barrel, then it is free floating. Free floating increases accuracy since it does not allow deflection of the barrel do to hand pressures, bi pods, slings, etc. The harmonics of the barrel are not interupted by irratic outside forces, much like what happens if you touch or don't touch a tuning fork. Free floating also assists the barrel to disapate heat away faster. Since the heat is not directly traveling into the hand guards and then directly back, hence more air to cool and not having a traveling circle of direct heat, just radiant heat which is not as hot as direct heat. Dimentions of metal change, so a cooler barrel instead of an overheated one gives more accuracy and also longer life the the barrel.
Hope this helps a little.
Good shootin, Jack