I think I have a great analogy.
Imagine firing a rifle but with a mount on the front end and the butt resting on your shoulder. You've lined up the target perfectly and then close your eyes. If you can stay perfectly still while your finger pulls the trigger, you've hit your target. However, when pulling the trigger, your body sways ever so slightly, your knees bend ever so slightly, you'll miss the target. However, if your eyes were open looking at the target when this swaying action occurs, you can recalibrate and hit your target.
Hence, if you have absolutely an impeccable stroke, you might as well close your eyes when shooting (look at the blond, look at the cue ball, etc.). However, if upon the final stroke, your backhand swings ever so slightly, you'll need to be looking at your target (i.e. the line of aim, un-focused view of the shot picture, etc.), to correct for the ever so slight problem with your backhand.
This is why, I think, pros (including Colin) with beautiful strokes can look wherever while amateurs may need to look up at the shot picture upon stroking. I think looking at the OB last in isolation is no more valuable than closing your eyes (except, perhaps, on a straight-in shot)...looking at up at the shot picture is what matters. Based on this, the learning curve to develop a flawless stroke may be faster by looking at the CB as shots will be missed due to flaws in the stroke.
My 1.5 cents. I realize that I'm not really stating anything that hasn't been stated already, but hopefully I've compiled it in a different way.
Dart/gun analogy to pool is not directly comparable. You look at your target in darts and shooting because it is impossible to keep your body, arm, etc. perfectly still and in line and you need to adjust for this movement. When shooting a cannon, however, which doesn't rely on body location on firing, you don't look at your target (just light the fuse). In pool, in probably depends most on your fundamentals although I'd argue it's impossible to have an absolutely straight stroke, but the pros have developed it enough where correcting any swaying motion (via looking at the target) isn't necessary.