A way to express the sentiment that tracer rounds might make it easier for you to hit a target without an elaborate sight, but in the process also betray your position to anyone who might be watching.
In WW2 it had been found out that tracers can be really bad, especially when used in excess. The ammunition strings used on B-17s had some 5 to 10 rounds of tracers at their end to signal the gunner. Of course, all enemy planes in the vicinity were overjoyed about that service.
Another big negative of tracer rounds was also discovered in WW2. Bombers' gunners had very little luck in hitting enemy fighter-planes since they tried to home in using the obvious tracers instead of using their sights and guesstimating a deflection angle. When the tracers were removed, it turned out that the gunners were quite good at hitting enemy planes but had been fooled by the deviating ballistics of the tracer rounds.