What is the purpose of the letter (suspected landing paper) given to international students by the Canadian Immigration Bureau when applying for a visa?

When students who immigrate or study abroad go to Canada for the first time, they give you this landing paper to prove that you landed in Canada that day. In the future, they will often ask you about the day when you arrived in Canada, that is, the day when the paper was confirmed. So it's best to save it for later.