Apparently, Intel's RST is not just RAID, but it's also supposed to help when a laptop is equipped with two storage devices, one small and fast (SSD) and another big but slower (HDD): https://superuser.com/a/1578326
IIRC there were Dell XPS models like that in the lower price segment. Never tried one personally.
Obviously. But why did they care to equip this laptop with the RAID by default?