It allows people to treat memory on the GPU just as they do on CPUs. You are correct, you will probably not achieve high performance if you are paging in from d

It allows people to treat memory on the GPU just as they do on CPUs. You are correct, you will probably not achieve high performance if you are paging in from disk all the time. But, what if you want it done once every ten minutes? Consider the amount of programmer effort required to do that manually. This is part of sharing the virtual address space.