Johnny, you can gain a deeper understanding of the meaning and importance of time/impulse coherence by reading this article:

http://melhuish.org/audio/article3.html

Thorsten, if I might quote from the above article:

Taking this to its logical conclusion, this suggests to me that for the realistic reproduction of a musical instrument (or any other sound), we should use a single transducer, period, i.e. mono, not stereo.

By employing stereo transducers, we gain the creation of a soundstage but we inevitably blur the upper harmonics of each instrument and thereby lose the realism.