What does the Academic Integrity Policy say about multiple submissions?
Appendix 3, Section 7:
The submission of an assignment, report or essay, which has been submitted at an earlier date for a different course, is an act of academic dishonesty unless the instructor has specifically authorized it in advance. The submission of the same essay in each of two courses, which are being taken concurrently, is acceptable only if both instructors have given prior approval.
Why is this academic dishonesty?
The work done for each course is expected to be original for that course. Once a paper has been submitted and graded, it is no longer original and cannot be submitted in another course. If a student wishes to use a paper from a previous course, they must ask permission of the instructor in the second course. That instructor may give permission for the paper to be used in some manner, likely as a source, and any direct quotes or paraphrases would need to be referenced properly.
When a student is registered in a course, the course outline details the work (and learning) required by the student for that course. If a particular course requires a mid-term, an essay and an exam to be written and a student simply re-cycles an essay from a previous course, they are avoiding work (and learning) and gaining an unfair advantage over other students in the course.