ORIGINAL: Bren Gun
Thanks. The part about using common sense when you said shorter cable runs don't matter much: what would you exactly fill in there to elaborate it? I might be missing something.
All else being equal (which it never is), the longer the cable run, the more room there is for noise to get introduced, and the more benefit there is to using balanced cable.
The only purpose of using balanced connections is to reject electrical noise, such as from nearby power lines, motors, flourescent light ballasts, CRT screens, radio waves, and so on. If there is no electrical noise, there is nothing wrong with using unblanced connections and cable. In fact, strictly speaking, unbalanced connections are actually better because they remove the additional stage of the balancing/unbalancing transformers. However the vanishingly small tradeoff is almost certainly worth it, and in practice, balanced connections are generally regarded as better all-around.
Common sense plays a lot in minimizing noise and signal quality problems. Every place and wire run is a little different, and trial-and-error and careful, critical listening are the basic requirements. The more an engineer understands about the technical aspects, the easier and quicker they can assess the situation, but at the end of the day there is no way to "think it through" to a certainty-- you have to actually listen and see what it sounds like and make some judgement calls about what comprimises are acceptible and where to draw the line between perfect and practical.
Cheers.