In Elements you didn't have the chance to save something in a .psd format. But in Photoshop you do.
Question - Apart from saving on space, which I see that it does, is there any reason to save it as a .psd rather than a .tiff.
I know that at one point when Adobe were trying to take over the world, we were told that we have to save everything in .dng, .psd as that would become the industry standard. Well, there's no sign of that happening yet!