What people write when they don't actually have anything important to say OR they believe their argument is superior (but can't prove it).
Either way it is an easy way out and a lazy move. People use it to bluff others by pretending like there is much more to say, when in reality they can't think of anything to add that is important or useful.
Mostly used by people who desperately want to feel superior, but lack the actual supporting information to be superior in an argument (or even contribute).
When you say "nuff said" you are letting people know that you are not able to have a normal conversation, and cannot accept anything against what you believe.
The *gun name* is the best gun in the world right now, nuff said. (Source?)
My *car name* is faster than yours, nuff said. (Why?)
*Game name* is the best game ever released, nuff said. (Stupid)