Single view allows a course instructor to view either all the grades of one single user(1 below) or a single grade item for all users (2 below):

When editing a grade or feedback, you can press tab to go to the next row below.
Single view may also be accessed from Course settings >Grades overview>Single view, from where the instructor is presented with a dropdown menu to select either a grade item or a student.
Grades may be excluded or overridden and modified. It is also possible to bulk insert a grade, which might be useful for example if you wish to give the grade 0 to all users who did not submit work.