Discussion pages are an integral part of a wiki; they are a place for users to decide which direction an article should go in, what to include and not to include, and to place any other kinds of comments. User message walls are also important, being a place where users can communicate about a wide variety of things, as well as receiving warnings from other users regarding unhelpful edits, and messages from admins about blocks.
These comments may end up outdated and seem useless; however, there are many reasons to keep them.
So why keep discussions?
There may seem to be no purpose, but keeping discussions can be very useful. For example:
- Keeping old discussions may prevent the same debate from happening repeatedly. For example, if two different sources provide differing information, leaving the discussion may prevent it being brought up repeatedly.
- Providing a record of a user's actions and discussions with other users. Although it is possible users with certain privileges to view or restore these removed message, it is much easier for anyone to be able to see these at any time.
When does this not apply?
Obviously, some discussion may not necessarily be an integral part of the article's talk page or user's message wall. Spam, or an utterly pointless message, however, is the only thing which can be deleted, as it is not actually a discussion of any kind.
Some other situations and what to do:
- Blatant flaming (negative and non-constructive, or offensive messages directed at other users) can be removed
- Talk pages that are outdated or very lengthy (these can be archived instead)
- When a user adds a post to an archived discussion, it can be deleted, depending on the situation.
Enforcing this policy
DDD is usually broken by new or unregistered users who simply do not know any better. Undo their deletion (but remember not to delete anything new that they may have added, like if they deleted an original post and posted a response to it) and tell them that they violated DDD on their talk page. However, make sure to provide a link to this page in that post, otherwise DDD will sound like meaningless gibberish to them.