Every time I am asked about decision making, I remember a mantra one of my earlier bosses use to chant all the time A company is not a democracy . Many modern managers have taken the completely opposing position of managing by consensus.
Personally, I believe that there must a be balance in all things and this is no different. For those times when a group decision is required, when is the group too big? Marcia W Blenko, Michael C Mankins and Paul Rogers wrote an interesting piece called Decide & Deliver: 5 steps to Breakthrough Performance in Your organization . An interesting statistic that they present is that once a group exceeds 7 people, each additional person reduces decision effectiveness by 10%.
The math is powerfully simple. The next time a group decision needs to be made, I guarantee you will see it in an entirely new light.