Q. Should I leave two tracers at the bottom of my magazine to tell me when I'm out of ammo?
Do you also want to tell your enemy both where you are and that you are out of ammo?
While technically tracer rounds are only supposed to "light up" a few dozen yards from the shooter, in actual use, many tracer rounds ignite right out of the barrel. This, combined with muzzle flash, is a positional dead giveaway.
Tracers are best left for machinegunners, or for squad/platoon leaders to use as marking rounds to direct the rest of the squad/platoon to a target.