In a recording situation involving multiple microphones in a single space the sound from one source may bleed or leak into the microphones intended for other sounds. This can lead to a degradation and muddiness of overall sound quality due to frequency colourations as a result of phase cancellations. This can lead to a problematic lack of separation of individual tracks during the mix phase of the production. 
use directional microphones microphone placement; taking advantage of microphone response patterns to reject unwanted sound sources isolation