The person that said to replace them is not making sense. *As long as
they work, why replace them. *Some people like to waste other people's
money. *

Obviously you NEVER had a fixture failure, were unable to turn off the
water and then had a flooded basement found main valve was bad

Or nearly as bad a line split under your kitchen sink, find the cut
off valve bad, rip the handle off trying to shut it all the way,
failing no water till the next day, since the main valve had to be
off. at midnite........ so fun

such experiences lead to preventive maintence, the replacement over
time of all valves with ball valves and adding extra valves, for
easier isolation of each fixture.

since these valves are used so infrequently you dont know there bad
till you need them the most

I didnt replace them all at once had a plumber do some in bad
locations like right on top of our steel beam, in a cavatity, others I
did myself or part of a larger project like a bathroom rehab.

homes require continious repairs to keep them up to date and working
well. you may call it waste, I call it dependability