If there's no question in your mind you can hit the animal in the cranium, take the shot. Personally, I only take those shots at about 100 yds or less and with a good rest.

You also have to remember the head of ANY animal is the most animated so getting a still shot is difficult. IMO, it's up to you, but I don't like them and usually end up finishing a deer every couple years that has been shot in the snout or jaw.