It depends on what kind of shooting you are doing. In many "tactical" style match stages where you are transitioning between far-apart targets and such under time pressure, I would say 'yes' -- for me 20x would take too long to "find" the targets (for < 600 yards in such situations, I'm usually around 12x), zooming in and out too time-inefficient (even with a switchview type lever), and 12x or so is plenty to hit 2 MOA+ sized steel.
For me, personally, learning to back off on the zoom in many situations has been one of the more valuable experience-taught lessons that has made me a better shooter (not that I am anywhere near the top in most matches, but "better" is better).
Also, unless shooting paper for high-precision, or shooting pretty damn small steel, I can't imagine the difference between 12x and 20x being all that helpful in terms of practical precision. I suppose it could be helpful in some field situations for discerning partially obscured targets if you know about where they are.