Deleting posts can really screw up a thread. If one of the "key" posts is deleted it could make the thread seem really strange. People will quote parts of a post or talk about something that is in the post...and if it is not there, well you can see where that will lead...LOL
If it is the first post in a thread I think if they delete it, that will kill the whole thread. Not too sure.
I have seen it happen on many forums. I would think that if you may have posted something in error you would re-post a retraction to clear it up. If it is something that you didn't want to post and did so by accident, then I would talk to the Admins about it and they probably can do something for you. It would probably be best to just have them delete the entire thread.
125 Gal-35 Gal Wet/Dry-Tetra-Tec PF500 HOB
(3) AuquaClear 301 Powerheads-600 GPH
Automatic Tempature Controller
5-6 Inch Sand Bed-200+ lbs of LR