I've recently reached enough reputation on one of the sites to be able to cast delete votes. I am not sure when a question is supposed to be deleted as opposed to just remain closed.
What criteria should I use when deciding whether or not to cast my delete vote?
Questions should be deleted when their content no longer adds anything to the site. Questions are closed for a variety of reasons, so let's look at each close reason and whether they should likely be deleted:
It depends; Look at the context of how they are asked.
You'll want to keep the question if the wording provides another way for a search query to find the content. It's a bit like a "see also …" entry in an index.
Delete it if the duplicate does not add terminology or alternate phrasing to find the question. It may not be worth cluttering up the system with this exact duplicate. There are several poorly phrased questions that will not direct traffic to us.
Almost always delete it.
Off topic usually says "This shouldn't have been posted here in the first place." So, for anything not about topic [x] or the off-topic reasons, just let it burn!
Delete it if it says "this is nothing but a 'broken window', and we should get rid of it." This includes lists of questions where the only information is about 2 lines of text per answer or Wikipedia/internet dumps.
Broken window theory: The theory is that minor forms of bad behavior encourage worse ones: that a neighborhood with lots of graffiti and broken windows becomes one where robberies occur.
Always delete it.
Closing it before deletion provided ample time for the author (or community) to fix it up. If it wasn't re-opened by this time, it should probably go.
See "Too broad".
If it's closed, it's fair game: vote to delete unless you can see that it has some value for the site (in which case you should probably vote to re-open).
The exception to this (and it's a big one!) are questions closed as duplicates. These can act as "guideposts" to direct users to a question with answers. If the closed question itself has answers, then flag it for moderator attention and request that it be merged - merging migrates the answers to the original question and leaves the duplicate question, locked, to guide future readers.
It pretty much comes down to if you think the post is helpful on the site or not. I normally limit myself to deleting blatantly off-topic posts or actual spam; if I have any doubt as to whether a post is useful I'll leave it alone. When I first discovered I was limited to 3 delete votes/day I thought that was incredibly low (in my mind I compared them to 12 close votes/day) -- I've never run out. Generally moderators delete the incredibly off-topic stuff before the 2 day waiting period is over, and spam flags take care of the spam posts
One thing people seem tempted to delete that you shouldn't are duplicates; if a duplicate is posted it's because that asker phrased the question differently enough that SO couldn't find the matching post automatically, so there's a good chance future users will search for that same problem using that same phrasing, and it's nice to have the closed post there to direct them to the right place
As per Jeff's post here, and answer here:
Questions which contain useful content contributed by your peers should generally be merged, not deleted.
I wish people wouldn't delete questions with good answers. You're destroying the useful contributions of your peers!
It's all about usefulness. Many questions get closed, but have useful answers that we want to preserve. Deletion votes should be based on usefulness, and that means usefulness to somebody, not just because it doesn't apply to your individual programming needs.
If a question is useful, but fits one of the close reasons, and has no potential for really useful answers, then it should be locked.
