I have 2 CX bikes, one with a single and one with a double and they both serve a specific function.
The double is used for commuting, training and in the pits. I like a double on this bike because I use it for a wider variety of riding. Some intervals just need a 46/12 and some climbs on my commute need a 36/25, so this set-up is useful. I only change bikes in the pits if I have a mechanical, I have never changed mid race just to get a clean bike.
When I am racing I prefer a 42 single with a 12-25. I chose a range that allows me to use all 10 gears at just about every race and also has a max 2 tooth jump from gear to gear. This set-up is simple, I never worry about shifting problems and I do not have a bailout gear that allows me to rest which forces me to push myself to the limit.