A similar meta post asks how much research should be done to prevent closure. The 1 answer (with 1 vote currently) elluded to "it's up to those with the closing privilege". Hopefully this question won't recieve an arbitrary/subjective answer and we can settle on some rule of thumb for the difference between the tag, and the close vote.
When should we add a homework tag instead of closing the question?
I think homework questions have a place on this site. Not everyone has access to text-books, and Wikipedia can get very complicated very quickly. Sharing expertise on the best way to do an assignment may help not only the student OP, but also many other students struggling to grasp concepts or finding an entry point to the content.
I recently answered a question about an MSA assignment. This is clearly homework from some course or other and has the homework tag. I was half expecting to see it in the review queue for closure.
An example of a similar homework situation that was closed was someone asking about dilutions. That question had the "homework" tag and was still closed. The list of closing as homework despite it having a homework tag is long.
We talk about "homework questions" a lot, partially because we get a lot of easily researchable questions from inquisitive people who see this site as a first port of call, partly because we sort-of disagree about when to close questions as "homework", and sometimes because we get people struggling with homework assignments who are essentially asking us to do it for them.
When the tag could be used without closure
- Should it be the focus of answers to introduce generalisations if possible, avoiding the need to close a good enough question? (The dilution question top answer could have used algebra rather than numbers for example)
- Should there be an attempted answer/research present in the question (refer to this question to see why this is iffy)?
- Should there be a threshold difficulty of questions that remain open? (I super don't agree with this one and think the egg question was a bad question, but on-topic.)
- Questions that are transparently open about being homework should stay open, and answers could answer with tips and guides rather than a specific answer.
I disagree with most of those suggestions, but I hope we can come up with something. I'm struggling, and I am sure some others are too given what I see ends up in the review queue, of when to use this close vote.