Back when I was I nAir Defense (just after we’d advancer form coordinated rock throwing) we kept our radars silent to deny info on them from others.
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There is some logic to that. But you need to answer a simple question:
How do you know when to turn them on?
General aviation radar at distance. You leave your run of the mill systems on where they expect them. As soon as they “see” something you turn on the systems.
Intelligence, threat status stuff, diplomacy, spies... that sort of stuff.
I was in Fla, Cuban jets would overfly and we didn’t target them. Also in Germany- don’t think sov Union ever overflew us.
Yeah, a surprise attack is possible, but other people decided how likely that was.
My memory is a littlw fuzzy, but I think the big deal for us was keeping them from knowing which of many frequencies we were using.
Today’s radars are very different I’m sure, but operational info would still be protected.
How do you know when to turn them on?
When you passive systems tell you to.