1) Server space is not an issue with us, CPU cycles are what's important. Thanks for wanting to help though.
2) There are consequences for deleting posts - such as if it's the first post in a thread it will remove the entire thread. And if people have responded, that's B-A-D.
3) If everyone could delete their own posts, they could say some asshat thing, piss someone off, and then delete it before moderators can see the proof of the asshat comment.
If you want a post of yours deleted, just PM a moderator and kindly ask or use the report this post to moderator link