Tracers were used extensively in machine guns in World War I, and usually loaded every 4 rounds in ground guns, and every 2 or 3 rounds in aircraft guns.
A disadvantage of tracers is that they show the enemy the location of the shooter. As an old military proverb puts it, tracers work both ways.
Early tracer rounds often had different aerodynamics and even weight from ordinary rounds, so that over long ranges the stream of tracer rounds and the stream of ordinary rounds could diverge. This is less of a problem with modern tracer rounds.