For Coues I use a 4-12x42 VXII. I used to use a 3-9x40, but for my eyes the advantage rests with the higher magnification when hunting Coues. It stays on low mag unless I see a shooter buck on another mountain.

Other than Coues, I'm not sure 12X buys anything. Doubt it does much harm, either. I just keep it on low mag and don't twist the ring unless the animal is holding still and distant.