The same reason it matters if you are late meeting deadlines for a customer or your job, because there are consequences. Turning in a paper late to school may not cause you to lose a client or get fired, but the fact remains that something was required of you and it was not delivered. Imo, students should be thankful to learn from their teachers that "yes, there really are consequences when you don't perform in your role as expected", as opposed to learning this from their (probably previous) employer.
> I'd say it might equally mean not pointlessly throwing in the towel and phoning the rest in just because you performed poorly early on and (rightly) feel like it doesn't matter anymore.
The fact that some people give up because they weren't able to meet the requirements of a class does not justify lowering the requirements of that class for everyone else. You're attending a class, the class isn't attending to you. If that's unacceptable then it sounds like you're probably in the wrong class.
> Sure. Exceedingly rarely though, compared to school.
Right. Which is why it is valuable to learn about consequences while you're still "practicing" in school.
> Most jobs don't involve additional work after you've finished work.
You don't have "most jobs", so that statement is not based on evidence. Moreover, I didn't suggest that jobs require taking home work, simply that homework for students reinforces the idea that work will be expected from them. You mention how stress negatively affect people... can you imagine how stressed out a person who has never done homework in their life would be if they were suddenly given a huge workload? Contrast this with someone who is used to spending hours on end studying, for whom the task would likely seem much more surmountable.