Not to. Or, at least, that'd be my advice. Unless there's a very specific reason you need to set your drives up that way I wouldn't bother. You're adding a point of failure for the convenience of not managing more than one volume.
My preference is applications and so forth sit on my SSD but file storage (music, archived documents, etc) sit on my HDD. Distributed points of failure, best performance. This also has the benefit of only reading from the HDD when I actually need something, aside form constant small reads for music and the like.