If you drain enough water from the boiler, you wan't have to shut off the valves at the top and bottom of the glass gauge. The valves could end up leaking if you mess with them.
Same reasoning why I don't use the shutoff valves below the sink if I need to change a washer in the faucet. I know from experience that if I shut the supply line valves under the sink, I will have to do two repairs. I only use the new shutoff valve at the meter. My thought process. Works for me.
