I have tried to use this functionality and get a lot down-voted a lot. When I said about this feature then I some people reverted their down-votes.
The thing is: Those questions you ask and answer yourself, they should be actual good questions that would be accepted by the community even if you didn't already have an answer for them.
The MSO topic Etiquette for answering your own question doesn't mention this, of course. It's from 2009 – please don't take it as the ultimate reference. Also, it was talking about answers posted much later, which implies that your question had to "survive" until then, so to say (i.e. not be closed, deleted).
Also, Jeff's blog post clearly links to his own question on Super User: Disable Java Plugin in Google Chrome? – now look at your question. Do you see a difference? Here's your question:
What is difference between unlink and unset in php?
Oh, wait. That's it? Let's assume you hadn't posted your answer below. Would this be considered a good, on-topic question for Stack Overflow, showing research effort? I guess not. Only seein the question, there's context missing: Where's your code? What's your actual problem with these two keywords? Why did you confuse them and in what situation did that occur to you?
This is why it's downvoted. It's simply a terribly bad question, sorry.
Of course, we're trying to share knowledge. But knowledge on a Q&A site means: in the sense of providing solutions to actual problems. Creating wiki-like answers or replacements for simple PHP documentation with a set up question is encouraging others to flood the site with equally bad questions – even though they don't have an answer yet.
If you feel like you always have to point others to Jeff's blog post that explains answering your own questions in fear of being downvoted otherwise, then there's something wrong with your question and you should probably fix it.