Allowing view all
By default, students cannot view the submissions of their fellow students.
If you turn this option on, then students will be allowed to view submissions of all other students enrolled in the same course. This may be useful if the teacher wants to encourage students to do better work in an interactive process.
The link to other students' submissions appears on the assignment view page only if a) the student submitted his/her own work AND resubmitting is not allowed, or b) the page is being viewed after the assignment deadline (regardless of the student's own submission). The submissions are listed by achieved grade (from the highest).
Obviously, this option is not relevant for offline assignments.