By having ability to substract a penalty or add bonus points to the calculated grade one can add weight for unforeseen (good) stuff.
It may also be used to model things such a “zero-sum game” where a reviewed submission takes points from the review submission.

Relates to:
Cheat button / Subtract points from grade

Submitted by Elmer van Chastelet on 2 December 2015 at 10:11

There are some assignments, where you can foresee this. For example, if a Java assignment requires a particular kind of implementation. In A&D, we have assignments where students are not allowed to use certain API calls, or where they need to implement an algorithm recursively. Currently it is not possible to give low grades for solutions which pass all tests but do not follow the policy, and low grades for solutions which do not pass many tests but follow the policy. With the current check lists, one of these two cases gets a high grade.

Postponed, might become part of more flexible grading schemes (e.g. weighted checklist items)