In my basement the pressure release valve, right where the water comes in
the house, gave way. Started spraying water all over the place.

I immediately shut off the water with the cut off directly below the
pressure valve. That stopped the spray, but water was still running at
about a gallon every 10 minutes. I opened a tap in the basement and one
outside. But water was still running. Called plumber. He said that PRV
was gone, and it looked as if my shut off was gone/leaking too.

He instructed me to turn off water at the street, and he would be here
tomorrow to replace PRV and add a secondary shut off.

The next day, plumber shows up replaces PRV and adds new shutoff above the
PRV.

He then tells me there was nothing wrong with my original shutoff.

I asked him, why then did he add a new shutoff, if mine was already working,
and why did he add it above the PRV? What possible use could that server.

He told me that with the two shutoffs, I could isolate my PRV.

Is that something I would ever need to do? Did plumber do me a favor by
making my situation better, or did he sell me a $150 useless shutoff just to
make a buck?

Thanks

Bob