Scenarios: If there is a change in course/lesson/quiz properties related to grading specific like 'Auto Award', Item Gradable/Non Gradable, Quiz weight change etc.
If you want to apply those changes in existing users grade those have completed all items you should reapply grading.
Steps 1 - Search for the user from user list. Click Transcript link to access user's transcript page.
Step 2 - Transcript Page - Select the course session from Enrolled course session drop down and click 'View Grades'
Step 3 - Click Apply Grading to adjust user's point affected by course grading change.