Well, there's always a non-zero risk you break something, especially if the system is older and things don't come off easily. The fun starts when you install th

Well, there's always a non-zero risk you break something, especially if the system is older and things don't come off easily. The fun starts when you install the new valves and re-pressurize the system. It's not difficult to introduce leaks, and I can tell from my personal experience that you will not enjoy it when it happens. So I completely understand why most people would prefer to just replace the knobs.