The argument in favor of a homework questions tag is that some people may want to hide them. For example, some users hide united-states because otherwise it dominates the page. Similarly, some people may want to not see homework questions.
It also expresses that the question will be in a slightly odd form and pushes back at the asker to make that homework question like others.
Example homework question:
Name five countries with constitutional monarchies.
Obviously that's a horrible question. The user hasn't done any research, as that's a trivial question to answer via internet search. We could mention that in the tag wiki excerpt.
For questions relating to class assignments. Please show what work you've already done. If none, do some first. Questions should be narrow and specific, covering just what you weren't able to learn by research. Do not expect us to write your answer for you.
Perhaps the text could be polished more, but I think that expresses the basic idea.