Different views on insulating inside walls for noise

I mean, I got into a chat about this with a regular at the bar who does insulation. One side says putting insulation in interior walls is smart for privacy, like if you have a home office or kids' rooms. The other side thinks it's just extra cost and time since it doesn't stop heat loss. Maybe it's just me, but I've heard stories where it really helped, like in a duplex to cut down neighbor noise. But then some installers say they avoid it to keep bids lower. What do you guys in the trade think? Is it a good add-on or something to skip?