Incremental is never incremental forever (restoring would be a nightmare and very risky).
Incremental mean that you perform, let say, one full back-up on Sunday night, then one incremental backup each day of the week but then, next Sunday, you perform one full back-up again. This aside, you may decide to keep one, two or more full back-up...
Incremental or differential is also something to distinguish in order to defined the right save/
restore strategy