When I fill up a question form, I see an
Answer your own question
What are the differences between checking and not checking this option?
If you check it, a new edit box appears and you can directly add an answer to your question. Both get posted the same time.
This is used to add a question you already have an answer for. You can do this for questions you think are helpful for the community and were not answered before.
Did you try it? If you want to answer your own question you can check the box so that you will get text area to add your answer. By default the textarea is not visible. So to answer your own question while asking you can check the checkbox.