It's more than just for cryo-freezing and attacks like that, it also helps defend against row-hammer and other DRAM refresh related issues since the scrambling means that the host kernel or application can't determine what the physical bits on the chips are going to actually be and end up determining the layout in a way to flip specific bits. It might still be possible but it's yet another layer of defense against memory related security problems.
Oooh, I saw this memory scrambling trying happening on the Open titan chips and I couldn't wrap my head around why they would scramble the memory since on read you descramble it anyway through the circuitry. That makes sense! Thanks for the explanation.
RAM crypto mitigates side channels.