if you had to have someone tighten the packing nut, then you saved the cost of the new valve, but spent a lot of money needlessly. A gate valve has a "wedge" and a "screw thread" inside it. The wedge can jam when it is turned off, and if the screw has been weakened by exposure to the water, it may break when you try to open the valve. In that case, you will not have any water until it is repaired or replaced. IF the screw becomes corroded with the valve in the open position, it could break when you try to turn the water off. That will mean you still have water in the house but cannot turn it off in case of an emergency. Ball valves do not have these two problems, but occassionally "jam" in the open, closed, or in between locations.