[ifoundthetao]

Maybe there are CRC values that signal hashes, and are used as such. So instead of looking at a message, it'll look at the CRC instead. This gives you the ability to not have to know the full message, but leverage this with part/none of it.

Another reason might be for QA testing, or for fuzzing purposes.

You don't always know the implementation details, but this type of control allows one to get more understanding of those details, by seeing how the software under test reacts. This stuff is not wildly uncommon in low-grade IoT devices, or high-end devices with a low level of security maturity.