I just noticed that I (as everyone else) can flag my own questions. There are fewer options (no "spam", "rude or abusive" nor "very low quality") to choose, but it's still possible to flag your own question as "should be closed" or "duplicate".
I don't understand, if that is the case, shouldn't I just delete the question? What's the purpose of having this options?
Duplicate questions are not deleted, they remain on the site as "signposts" to the existing answer that might be found by a Google search that doesn't find the duplicate question.
If you realise that one of your questions is a duplicate, it is a good idea to flag it as such.
In addition to above explanation by Blackwood, your question might already have fetched some comments or answers by others, so your question page now has their contribution also.
Thus, it would not be ethical of you to deny them the credit for their part of contribution by summarily deleting the question.
Thus, it is always better to have a second/ third opinion, in this case, by flagging the question to a moderator explaining them your reason why you think it should be deleted, and he can then unbiased assess other's contributions on that page and decide to delete or not.
