Computer Science tried a homework tag, we debated it several times on our meta, we found that people can't even agree on what the tag is supposed to mean, and we ended up getting rid of it through a vote. The only effect I've seen from getting rid of the tag is that it's cut down on the number of arguments about adding it to a question. In other words, all the homework tag did was to generate arguments about its use. Good riddance.
Let me emphasise a point here: even the supporters of the homework tag do not agree on what the tag means. We have a tag that means different things to different people, generates a lot of argument, and does not categorize questions (it is perfectly possible to have two identical questions, except that one has the homework tag and the other doesn't; depending on what homework means, they may or may not be duplicates). So the homework tag is both useless and harmful.
Even Mathematics's homework policy is far from consensual. In an old discussion on the topic, the most upvoted answer by far, by Professor JDH, reacts against the opprobrium against homework questions:
Finally, let me say that the policy of encouraging weasily half-answers to questions that have been deemed to be homework, consisting of obscure hints only, amounts to an annoying policy of encouraging bad answers here at math.SE, and I am completely opposed to it. For this reason, I think we should abandon or ignore the homework tag.