I will offer an addendum to those that offer up the theory of "doesn't hurt in the field". I agree with the part about not "feeling" the shot in the field. I wouldn't offer up shooting my rifle a couple times as proof though. I would however offer up a good Texas dove hunt when I might shoot 50 or 60 times in an hours time with my 12 gauge. Now before you go to thinking about legal bag limits, I tend to take shots that are not even possible and mixed with my poor shooting ability, takes that many to get my 12 or 15!!!
But either later that day or the next I am painfully reminded that even when surprised by a bird that comes out of nowhere, I really should wait until the gun is placed against my shoulder before pulling the trigger. I have had my arm bruised from elbow to arm pit as a result, but never noticed until later.

But I willtake exception to the "don't hear the shot and/or don't have ringing ears" comments offered up by some earlier. YOU may not notice it when shooting at game, but it does happen.
I would also add that the "blast" and "ringing" is exactly what prompted me toremove my factory installed muzzle brake and order a thread cap. My brother took his first Bull with this gun in 2004, he is a seasoned hunter of many differing types, and the flash/smoke/dust and resulting deafness for the next few minutes was strong enough to temper his euphoria over taking his first bull.
With two types of hearing protection (in the ear and muffs over them), was still too loud.
As I can't stand the thought of hunting while wearing hearing protection, the decision was made.

Personally, I would suggest to anyone that if you can't shoot the gun without a muzzle brake, don't shoot the gun. Only takes one shot to lose some hearing and it is cumulative.