No, it doesn't. In rare case, you may lose few of your activities. Otherwise, there's nothing wrong deleting your own post. Why though? I don't think there are a lot of reasons for deleting your own post.
There are instances that can make people delete their own posts. There was a time I had network issues and that made me post the same thing twice... when I noticed, I have to come back the next day to delete one of the posts.
I have also seen some people who made applications to different signature campaigns at the same time and when accepted in one, they delete the other applications. I would also love to know if this is a bad practice.
There should be other reasons why people delete their posts, but I just gave the ones I have experienced.