When faculty upload a file into an Assignment or Quiz that has a future available date set, the file is, by default, stored in the Files area immediately with a setting of published (unless faculty go and then change the file's permissions to "only students with the link" or put it in a Files area folder already set up with this permissions level).
As we have faculty who have the Files area visible to students, this can allow a student to view the uploaded file before its intended available date. As well, my understanding is that students using the mobile app get a Files notification sent to them, unless the faculty member first uploads it into a Files area folder with permissions of "only students with the link."
Ideally, the uploaded file's availability should align with the assignment or quiz into which it was uploaded. I can see reasons why the file may want to be visible to students after the due or until date of an assignment or quiz has passed, but I see a lot of benefits to aligning the first-available date.