My spotter is a Spider 5D so I'm forced to run TAG I think with ECM and the light profile of the spider it's very viable, I tried to fit a NARC on my Oxide but then it has too low firepower. I sold the mastered and upgraded Jenner D back when I was new and needed mechbays for new mechs, why oh why ?
Well the usual mistake people make in that position is to fire a laser with the tag so the person notices they're taking damage.
See this SOOO much. If you're trying to pick up the assist, at least fire so that your damage hits while the missiles are landing so the enemy is less likely to notice. And for love of Pete, don't stand in the same spot afterward!
I recently switched my ravel 3L up. I took off the TAG and added NARC. It's been a lof of fun actually. Especially over the weekend of challenges. NARCing the ECM and running back to cover my Assaults, blasting with 3 MLas along the way. Getting in behind them and popping the UAV, NARC the ecm or the DW and run away laughing all the way to the bank. Good times. To wit, I run TAG on my LRM boats. My spotting mechs are now running NARC for the fun factor. Keeps it interesting.
Easier, safer, and more fun to hit and run with a narc and lasers than to stand there with a tag and doing no damage yourself while that dual gauss sniper is aiming in on you.
On a light, i prefer NARC, since it lets you hurry in and hurry out, after tagging enemies, then your allies know where the enemy mechs are. TAG i use on some of my missile boats (Stalkers).