Q:

Why is this answer considered as a poor answer?

Would you kindly tell me why is this answer considered as a poor quality answer. I'm pretty sure the code-only answers are considered acceptable, so why isn't this one not acceptable?

A:

Rule of thumb: "No Action Needed" is almost always the wrong choice. 
   
Those blank lines are just there to let the first line sink in a bit, because... Yeah, that's not exactly obvious from the UI, eh?
But... "No Action Needed" is still almost always the wrong choice.
Unless you understand the answer - like, you're familiar with the topic, you know the problem being described, and can recognize that the answer not only solves it but explains the solution in a way that's nearly perfect - it's very unlikely that you can say with confidence that no action is needed. If you're unsure, the button you want to press is Skip.
For everything else, there's almost certainly some action that you can take. For example, a downvote. Or an upvote. Or an edit. Or a flag. Or a comment that reads, "Hey friend, would you perhaps like to explain how this code solves the asker's problem? It'd help, a lot!"
Or, some combination of those actions. 

