Sounds alot like what my Parents set up for my Grandparents before my Grandpa died, and that's usually to avoid taxes & the like on the estate.
The other big reason is to transfer the funds so that both partners can't get cleaned out if one of them get's ill in a very expensive way. The Government will take over, but only after all assets available are pretty much gone - what that means is that if you don't seperate the assets in some legal way, all of a sudden the surviving spouse (illnesses that expensive are almost always fatal) is completely and totally broke by the end of it.
You probably need a Lawyer to figure out exactly what it means. We needed one (my Uncle on the other side of the family, actually) to set up my Grandparents. I only know anything about it because the trusteeship devolves to me in the event something ever happens to my Mother. Actually, it's joint with me and my Uncle then. My Grandparents didn't trust him to have Trusteeship by himself, so they threw me in there if something happens to my Mom.