This is from something I'm reading, what exactly isn't important. But it does explain why understanding punctuation and doing the proofreading matter.
And he had been good, no more than that, a talent to be reckoned with.
Really? He'd been no more than good, but still so fabulous? This doesn't make sense, one part contradicts the other. Or maybe he's getting by on other attributes than his skill.
This is what I think the author meant:
And he had been good, no, more than that, a talent to be reckoned with.
Now he's all sorts of top flight! And my perception of the character is really different.
Next time someone thinks editing and proofreading shouldn't be counted for a rating, remember that one little comma can completely change the direction the story's going.