breaks down stuff holding the meat together. 

similar to aging a piece of beef. 

You can taste the difference. 

You never ever see a real chef cooking anything frozen except ice cream. 

I have baked chicken pretty much half frozen.  I think this is how you get that taint of blood next to thigh bone.  Years ago I started cooking only when completely defrosted. 

I can't cook pork and don't even try.