To be fair, Lou, we now know that a lot of what Willie "taught" in the little red book, 1.) isn't what he himself used (what he shows/poses in the pictures for, isn't what you'll see from him in real life play), and 2.) isn't what is commonly taught as "standard template" for foundational play.
There are several good examples of this, but two off the top of my head are his grip and his bridge -- what he used in real life, and what he poses/shows in the pictures, are two different things.
I wouldn't go as far as to say "detrimental" either. As long as you can pivot at the shoulder (drop the elbow) perfectly in-line with the shot everytime the cue makes contact with the cue ball, there's nothing "detrimental" about that at all. The problem is that's a variable -- that's something else that can go wrong, rather than keeping the movement simple by moving only one joint in the arm. The shoulder is a ball-and-socket joint, able to move in any direction; the elbow is a hinge that only moves in the direction of the cue delivery.
It's not a "detrimental" question as much as it is a "keeping it simple" question.
I drop my elbow, too, when I'm really powering into the cue ball -- it's the natural after effect of the momentum of the forearm moving forward at high speed. The elbow drop is not as pronounced as, say, Mike Sigel (mine is only about one or two inches at the maximum, whereas Mike's whole arm almost "folds down onto" the cue).
I get what you're saying, though -- the "effort" of trying to pin the elbow can take away from the sensitivity in how hard the cue ball is hit. I guess the trick is to find that happy medium.
-Sean