When not using Require students to click the submit button, the student can edit his submission even after it has been graded (if no cut-off date is set and passed).
To me it seems just like a way to open up for problems, so I'd like to know the user case(-s) for that.
If one wants a formative assessment, it is better to have the student click the submit button and re-open the assignment for another attempt, thus getting a good history of the submissions.