A low impedance mixing console output can easily drive a dozen power amplifiers. In most cases, this can be handled by a passive splitter. But do not forget that a short circuit at one of the outputs will be transmitted to the other outputs by the transformer, interrupting or, at the very least, weakening the total signal. Decoupling resistors can reduce this effect but will also cut down the signal level.
Microphone signals, which operate at extremely low levels, are more susceptible to interference. Active splitters are preferable where longer cables are used and where professional standards are required. There are obvious advantages here. The “plug box” is located on stage near the microphones, so only short cable lengths are required. The active splitter can also boost low microphone signals. This considerably improves the quality of the signal before it is transmitted along the multi-core cable.