My first dog was free fed. She was the kinda dog that would rarely eat. The only treats she liked was a rawhide and some milkbones. She never seemed to lose weight nor gain it except the initial few weeks we had her from the shelter and she even looked a little pudgy even though she ate so little.What I found funny was she was found a stray so you would think she'd eat everything she could.
My second dog is NOT free fed. She would eat everything in sight and throw it up then re-eat it if she could. Plus, she would end up pooping all over the house if she ate that much. I know this because she has gotten into food before, then would poop in the house after that. Also, she has a conformation to many dog prone to bloat do, and like said above, it could be hazardous to her health if she ate that much (plus she'd be really really fat

)
As far as training goes with food, I do on occasion tell her to sit/stay and go about pouring her food into her dish and when I tell her, then she can go eat. I think that is a good way to teach a dog to leave people foods alone (when you are there at the very least).
I agree with all of the above, it depends on the dog mostly, and the owner's preference too.
~MSE