It seems that U&L has covered this fairly well: Understanding UNIX permissions and file types, Execute vs Read bit – How do directory permissions in Linux work?, What are the different ways to set file permissions, etc, on GNU/Linux?, and more.  Do you believe that AU needs a separate copy of that information?  Is there something you would add for Ubuntu that isn’t already in the U&L answers?  If so, please add it there.

@Fabby: I believe that you missed the point of Zanna's comment. Your answer still says "flagging is better than deleting most of the time (The notable exception being off-topic questions: they should be burninated! ;-)".  It should say "deletion is better than flagging most of the time (The notable exception being duplicates; they should be flagged)."  If you realize that you asked a question that was unclear, too broad, POB, or based on a really dumb typo, then you should try to delete it (unless you can fix it). Also, you weren't clear that OT questions should be flagged for migration.

Similar discussion on Meta Super User: Concept of “conditional” downvotes?