Exiting Student Preview mode
When exiting Student Preview mode you are offered a choice to either save the data or not. If you choose to save the data, when you next enter Student Preview the previous data would load. Meaning if you had submitted a test, quiz or assessment, the system would remember that.
It is possible for you to submit an assignment as a student, then exit and save data. You could then grade the submission using the inline grading tools, or upload feedback. When you then next enter Student Preview you would be able to access the grade and/or feedback as a student would.
Below is a video showing exiting Student Preview with the option to save data.