I basically never use NARC. When I'm playing someone in person, we usually play 3025. When I'm playing Megamek with 3050 tech or later, I usually want to go with larger forces that I can't really play on the tabletop. At that point, I kind of rush through tactical decisions because I'm maneuvering an entire company or more. I don't always move perfectly, don't always make the best firing decisions, etc, because I'm trying to finish the game in a reasonable time.
But NARC does have its uses. The best thing about NARC is that it gives Introtech mechs a nice little edge. It's a cheap upgrade for a lot of second line troops. You should be able to retrofit the launcher onto a normal mech pretty easily. Swap out an SRM-6 on a light mech and there you go. C3 systems would be the same. Yank a medium laser, stick in a slave unit. Yank a large laser on another mech, stick in a master. You don't have to upgrade your whole force, just 3 or 4 mechs linked together become (potentially) much more powerful in the right situation, for not that many C-Bills.
Say you've got a company of 3025 designs, and here's a lance level C3 system, a NARC beacon, and some missiles that use it. Stick your NARC in something fast and light, like a Javelin. Its job is to stay mobile and hit the enemy's slow movers. Stick a slave in something that likes close-range, like a Hunchback. Two more slaves in missile boats, like Crusaders or Archers. And put your master in something that sucks anyway, like a Vulcan. Fight like normal, but have your missile boats positioned to shoot at whatever the Hunchback moves in on. And he moves to engage something that has already been NARCed. A move like that will ruin somebody's day. Big LRMs firing at short range (with no minimums) and getting a +2 on the missile chart? After a big AC has fired? That's a lot of benefit for a minimum amount of new tech. If I was a company commander, I'd be racing to install tech like that.
Background-wise, NARC would be one of the big reasons why militaries were forced to install so many ECM suites. It's the technological equivalent of a cheap shot. It's not that hard to counter, but you have to make sure you account for it or some jackass is going to hit you with it.