Beat,
Thanks again for your insight.
Parallel compression can also be used to altar a sound a little which means that it could be used as an effect as well (Dropping the threshold and lifting the ratio). But unless you're doing some avant garde kind of stuff I don't know if this "effect" application would be relevant in orchestral settings. Personally, I've been known to expirement a little by feeding horn ensembles, strings, choirs through various guitar amps just to hear the results. Every once in a while I am delightfully surprised of those results. Of course, that's part of the brillance behind using samples. Live players might not appreciate my sonic mangling of the hard earned sounds they produce.
I realize that you are not suggesting to use parallel cmpression as an effect but your detailed explanation gave me some ideas. This certainly is food for thought.
Thanks