I don't do it often, but I have done it a few times. I'm sorry :( I can't speak for others, but I can tell you the reasons I have deleted new posts: 1. Wanting to add something to it but being unable to edit it. So I delete it and post a new one. 2. Fights with the send button resulting in multiple posts being made, so I delete all by one. 3. As you stated, finding the answer soon after and prior to someone replying. The reason I delete these is because sometimes I feel like a nuisance and that I'm imposing on people. I only post my questions if I absolutely can't figure it out myself. Sometimes after a long time of looking without success I post only to find what I was seeking right afterward. A few times I've deleted the content of my post and put "found the answer". I do see what you mean about sometimes the question being asked could be of value to others, even if it's no longer of value to the person who posted it.

"It is good to see ourselves as others see us. Try as we may, we are never
able to know ourselves fully as we are, especially the evil side of us.
This we can do only if we are not angry with our critics but will take in good
heart whatever they might have to say." - Ghandi