As a TA, I have to grade students' assignments. The main instructor usually has requirements regarding the minimum average grade for the class. At the same time, it is tricky to predict the class' performance until I have graded about one third of the students' papers (for larger classes, and one half for smaller classes).
Even then, unexpected things can come up. To ensure fairness as well as fulfill the minimum average grade required by the instructor, I often have to re-grade their papers multiple times. For example, when first grading Josh's work, I gave him 4/5 pts for question 1. After finding out some others did better than him (but still not entirely correct), I gave the other students 4/5 and take one more point from Josh, and this process keeps going on and on. As a result, when I return the assignments to the class, their papers are full of my corrections for their previously assigned points.
I did mention curving to the instructor, but he didn't seem to be OK with that. In fact, he manually re-graded the first HW instead of curving it, which made me feel bad (and insulted). It doesn't seem like the students have an issue with the way I grade, but I still wonder whether modifying the grades multiple times make me look unprepared/unprofessional?*