I always leave a room neat, or at least as good as I found it. I also always want to leave all papers, completed during the day, graded.
This isn't always an easy task. Even in the lower grades. Different teachers have different ways of grading assignments, and if you write in pen on a student's assignment, she/he pretty much has to go with that.
Usually what I will do is look around, not snooping, for other papers that are similar and already graded. That way I can see their method. If it's something simple like math problems, I can just circle the wrong and put a
35 on top of the page. But what happens when a problem has two parts, or they are short answer. What is the teacher looking for? Spelling, punctuation, neatness, complete sentences, graphs, charts, showing your work? I hate to leave a lunch of work for her/him the next day, but what choice do I have? If I score it wrong, and it's an important assignment, I could be leaving them with a big headache.
So, my conclusion has been, no grading if I can't match up their work with something else. But I always leave fully explanitory notes and apologize for not grading. And hope that's good enough.