A gear drive replaces the timing chain and sprokets at the front of the engine. It is usually used when a camshaft can utilize a fair amount of valve spring pressure as there is no way for it to stretch and therefore retard the valve events. Using this setup to drive a mild street cam is a personal choice. Some guys just like them and are willing to put up with the minor gear whine. They are quite a bit more costly than the usual chain and sprocket arrangement, so that may figure in your decision.