why leave a tap on? When you turn the water off to the house

Why do plumbers leave a tap on with a trickle of water when they turn off the water to the house? Is it safe not to do that and leave the water turned off all night? I am tired and want to sleep and the basement is a horror story. I'd rather leave the water off and keep working in the morning? The dripping open tap noise will drive me nuts if I leave it all night. and I am not sure I got the temporary shut off valves tight enough not to blow off under full pressure.
Anyone know?
I had no idea getting old galvanized pipe to unscrew was so hard, after hours of wd 40, heat and hammer I finally got one loose enough that I could cut everything off above it. Only two more to go.
My daughter came over and started laughing. She said even when she tells people about her mother no one believes her. There I was on Sunday with guests just left and I thought "I'll just try that beep beep pipe one more time" so I was down the hole in the floor in linen and silk hammering away when she arrived.
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It depends.

I hope you're asleep by now, but if not, put a piece of cloth under the drip. If that is not enough, rubber band a piece of cloth to the faucet so the drip runs down the cloth to the sink.

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Maybe I should have said that if your main water vavle is turned off and yet water is coming out of that faucet, it's clear that your valve is not enough. If you close the tap that is now open, the water will come out whatever holes you have where you have been working. And I presume there is no sink under those places.

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If the plumber is going to work on the pipes, it is to let air into the pipes so they will drain.
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I don't know why plumbers do that, but I did just the same thing myself because the shutoff valve does not shut off the water completely. So I open the lowest faucet (closest to the ground) I can find so that water would come out of that faucet instead of the one I'm working on.
Then when I'm ready to test my new plumbing addition, I turn off that faucet but leave the house shutoff valve untouched. This would still stress the plumbing system, and if there is a leak, only a little water would come out. If there is no leak, then I turn on the shutoff valve.
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