A manual grade item populates a gradebook with work that occurs outside of Moodle:
- Work hosted elsewhere, such as required emails or outside tools from publishers (without setup or available plugins);
- Extra credit on top of normally graded work, such as a student earning 12/10 points on an assignment;
- In-Class work; there is also the attendance activity in Moodle;
- Pretty much anything else that no other Moodle activity seems to work.