I don't have enough experience with XMM registers (and SSE4 in general) to know if this is actually {useful,possible}, but a hypothetical use might be creating and using cryptographic keys such that the important numbers are never stored in main memory. If e.g. a decryption key is ever present in RAM, it's probably possible to steal it with a cold-boot attack that copies all of RAM. Once you have the RAM dump, the key can probably be found very quickly:

    for (secret_key_t *p = 0; p < RAM_SIZE; p++) {
        decode_with_key(p);
    }

This does require significant physical access, but it works. I seem to remember reading ~1.5 years ago about a turnkey forensics kit (bottle of refrigerant included) for doing cold boot attacks? Regardless, more ways to protect keys is could be really useful.

https://en.wikipedia.org/wiki/TRESOR