Well, my aim is generally poor, and if I miss on my first burst, it's nice not to alert the enemy to my presence with a few hundred tracer rounds flying past his windshield.
On the other hand, my aim is generally poor, and if I miss connecting with an enemy on my buddy's six, it sucks not being able to alert the enemy to my presence with a few hundred tracer rounds flying past his windshield.
So, really, I'm darned if I do and darned if I don't, but I leave them off, because with aim as bad as mine, regardless of where the few hundred tracer rounds go flying, they clutter up the screen so much that I find they just make aiming even more difficult for me.