During my time as a CGI I always advised students to keep their results sheets for future reference. Some did and some did not.
During that time the results sheets served the following purposes:
1. When students had passed all of their ground school exams some went off to do their flying at other schools. Some of these schools refused to start the CPL/IR flying training without proof that the exams had been passed. I frequently had to produce "emergency copies" for them.
2. Some employers require written proof of the exam results. Although I stopped being a CGI some years ago, I still receive requests from past students for written references including exam results.