ARM64: LDR (register) SXTX extend

Hi,

What's the purpose of the SXTX extend? I understand the concept of sign extension when, say, the source register is 32-bit and the target is 64-bit.

In this case, however, both registers are 64-bit. So what's the point? What can you do with SXTX that you cannot do using other LDR (register) variants?

Thanks,

Nikita