Follow-up: so periodically closing and opening the valves, even just a couple of times a year, helps prevent their getting stuck over years (as mine did). Also, if one valve isn't closing properly or is starting a tiny leak, you get some advanced warning.
If you do some home maintenance yourself, working value is useful for e.g. replacing the valve inside a toilet, or replacing a faucet. You want to cut off the water when you start, possible check, make sure it's on when you're done.
Our last apt, just after we moved in, woke up at 4am to the sound of water - toilet tank crack! Waterfall. Shutoff wouldn't budge. I held the lever in the tank up while husband found main shutoff.
When we bought this place, used quarter-turn shutoffs on sink/toilet water lines. Recommended.
For me, it was a water filter installed under a sink by a previous owner. One night we heard a sharp crack as the long-neglected filter accumulated enough minerals to force its way out of the holder. Thanks be unto shrimp Jesus that we were in town and sober and had a working shutoff.
Smart people - smarter than me - have an electric shutoff at the service point controlled by Zigbee moisture sensors everywhere that water might appear but should not. Costs couple hundred bucks, but cheaper than disaster.
Because if you don't then they suddenly won't budge when you need to close them, and then you grab a pipe wrench and the next thing you know you need a rubber raft...
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No problem since we shut off water in the whole building to replace the valves... but bad if we'd wanted to deal with a bad leak.
(Possibly decades of never being closed and opened)
We're replacing those stuck ones.
When we bought this place, used quarter-turn shutoffs on sink/toilet water lines. Recommended.