Diodes are often used for protection from accidental connection of the power with reverse voltage. But they either suffer from voltage drop for a series diode, or requiring a current limit, such as a fuse, for a parallel diode connection. A parallel diode also applies a small reverse voltage equal to its forward drop under short-circuit current conditions when the reverse voltage is applied, which may or may not be a problem for the protected circuit.
For minimum forward drop and no reverse...