You can set up the expansion card to act at a RAMDisk, or a swapfile if the storage card you are using has fast writes and a decent access/read write time. I believe class 6 or higher.
I would imagine it's similiar to ReadyBoost, however I have no idea why they would engineer this process and then neuter it by placing it on the expansion bus.
They should just carve out some NANDFLASH and use it instead.
But to answer your question, if you were using a system memory deficient hardware platform in a memory intensive environment, and you had the swapfile set up on the SD card, and you were using the SD Card as a storage repository then the answer would be yes.