Another use case for key zeroize could be a preemptive measure. After loading and decrypting the bitstream, the BBRAM key can be purposely zeroized before sending the system out into the field. Of course, this would only work for a system that is not intended to be power cycled after it becomes deployed (for example, a missile after being launched). This could also be used for an eFUSE key by writing over it with all ones via MASTER_JTAG before deployment as long as eFUSE key reading and writing has not yet been disabled.