There is some guidance at Help Center > Privileges > access to moderator tools:
When should I delete questions?
Closed questions that are of no lasting value whatsoever should be
flagged and deleted.
Before voting to delete, please check whether there are any good
answers; if so, then the question should be flagged for moderator
attention as a potential merge candidate. We don't like to lose great
Also, be cautious when deleting questions closed as duplicates; they
can serve as a signpost, directing users to useful answers on another
It takes 3 votes, minimum, to delete a closed question. However, the
number of delete votes required scales to the number of votes on the
question and all its answers.
You must wait for a question to be closed for 2 days before you can
vote for deletion. This restriction is removed for trusted users when
a post scores -3 or lower. If you feel a post should be deleted
despite having lots of votes or for being new, please flag it for
community moderator attention.
You can view a list of posts with outstanding delete votes via the
moderator tools delete tab.
Though IMO neither of the two categories picked out above ("any good answers" and "closed as duplicates") really applies for the tag (webapp-rec) you have chosen for your example - one that is appropriate because off topic now by definition but nevertheless very popular.
The same place though offers a link to a different, and possibly clearer, post about the Deletion process:
See also: How does deleting work? What can cause a post to be deleted, and what does that actually mean? What are the criteria for deletion?