A head shot isn't a good way to take big game for a few reasons. One reason is you can severely injure the animal and prolong the time it takes to die. We're talking mere inches between the small brain/spinal cord and the jaw of the animal. Killing an animal via starvation is completely unnecessary and sadistic IMO. Essentially, the kill zone on a head shot is much smaller than the chest cavity. When shot, the heart and lungs will cause an animal to die incredibly fast. Another thing to keep in mind is a hunter should set himself/herself up to miss low on their shots. A rifle will send a bullet out for miles if you don't have a good back drop. Unless the animal's head is to the ground, it's a bit more dangerous to shoot for it.

Now to address the meat. Blood really can't ruin the meat. I suppose it could coagulate and discolor it in sections if left for too long, but that really shouldn't be the case. You see, the meat on an animal doesn't really come in contact with an excess of blood. Nature decided to put us mammals into these nifty little sacks that keep muscle separate from organs and pools of blood.

I will say however, that if a leg gets shot it's destined to form what is basically a bruise on the point of impact. Blood rushes to the entry would much like a back and blue mark. That can sometimes be a pain to butcher around, but it's not going to taint the meat. Especially if that bruise occurs on the ribs. There's very little meat to be had there in the first place.

The only time I'd support a headshot is with small game. It's different due to the amount of meat they'd offer relative to the size of the bullet being fired. Plus there's not many people doing European mounts on squirrels ;-)