Harsh marking - is it worth complaining? I know that we have to be meticulous in pure mathematics courses, and I appreciate that. Comparing a particular course I took recently to the other pure math courses I've taken before, it appears that the marking has been unnecessarily severe. I had assignments which weighed 25% of the total mark, but the marker could almost arbitrarily pick what we would have had to specify in solving a problem. For instance, sometimes there were points in a proof for which it was not clear at all whether or not they should have been specified, since they were either evident (clearly, there were parts in which the marker was very fault-finding, not like in most other pure math courses I had taken) or were previously proved in class or in a previous assignment. The marking scheme was entirely up to the TA who marked the assignments, so that he decided which questions to mark or not to mark. There were usually 20 to 25 total marking points in each assignment, but some questions were deemed to weigh only 2-3 points, and the TA could easily deduct 33-66% of the mark for missing / skipping minor details of the problem, whereas the entire answer / main point was correct. The instructor had admitted during the course that either more total points should be introduced or partial points (such as 0.5) should be given, but that didn’t happen. Some questions weighed disproportionately many points, such as when in one assignment, which consisted of five questions and which was marked out of 25 points in total, one of the questions was worth 9 out of 25, and it was not the most time-consuming question. In the final examination, the marking style similar to that of the assignments was applied, and I’m convinced that it was too harsh.

I've discussed the exam results with the instructor, and I'm still convinced that the marking was not always quite appropriate. I also wrote an email to an advisor and he said that I could write a petition to reconsider the marking. But should I really do this? I feel that the department would not perceive such an action very kindly, and some talks in the department would probably follow. So I'm not sure if it's worth it.

Should I just move on and forget about this?
I disagree with aparente's suggestion that filing a petition is a good way to get the department to improve.  

Generally speaking, an instructor has a lot of latitude to determine how grades are determined in their class.  You can challenge your grade by a petition, but whoever considers the challenge will be inclined to defer to the instructor's judgement, unless the grading was blatantly unfair or unreasonable (some universities use the standard "arbitrary and capricious"), such that the grade wasn't really related to the quality of the students' work.  A grading scheme that is just "too harsh" or "too picky" isn't likely to meet that standard.

It also isn't really a good way to bring the issue to the attention of the department, due to the adversarial nature of such cases.  If the grade is upheld, as I suspect it would due to the required standard of proof, people may tend to view it as "the instructor is right and the student is just whining".  It will also focus the attention on you personally, instead of on the fact that this is a general problem affecting many students.

I would suggest instead that you mention this issue in your course evaluations, and encourage other affected students to do the same.  Explain the issue in detail and as objectively as you can, keeping the focus on how this affected the quality of the course, rather than on how it impacted your own grade. If the department cares about teaching quality, this will encourage the instructor to work on this.  If they don't, then there is probably nothing you can do about it in any case.