A couple of my dad's squadron mates are still alive because tracers were purposely thrown where an attacker could see them causing him to break off his attack.
Imagine how you would feel if you didn't have tracers in that situation and had to watch as your friend was shot down and killed because you selected to remove tracers from your ammo load out.
Many an enemy has been caused to break off an attack by someone who didn't have a shot but was able to throw out tracers that the enemy could see and scared him off.
