Yeah, as mentioned above, I find the concept far more applicable as a 'sighting device' for finding targets in your main optic quickly.
I use this:
http://wiebad.com/zen/index.php?mai..._id=45&zenid=433bc99718ecdef0dc3e2725e485cb50
That one is nice because you also get the bubble level, and they make a 35mm version for those of us with that diameter scope body (Vortex Razor).
Attach a red dot zero at 600+ yards -- during time-limited stages, I find it very useful both for transitioning to and between long range targets, and for re-acquiring a target that I "lose" somehow (someday this will happen less, but until then..)
Put the dot on the target, and the target will be in the scope picture, even at full mag (have used it successfully to 'find' targets out to like 1250 yards).
Sure, you can accomplish the same thing by either zooming out and staying there (which can sometimes make it harder to spot misses, etc), or by zooming out, acquiring, then zooming back in, but this is kind of best of both -- the tradeoff being the expense and a little extra weight bulk. I ditched scope caps and just use a neoprene Scope Kote that goes over the main optic and the red dot.
So basically it is a speed/convenience aid ... allows you to use higher magnification (which I mainly find useful for seeing my hits/misses better) and still acquire targets quickly without having to futz with zoom.