Hildon-desktop is responsible for the window management, so that itself you need to keep, hildon-home however is responsible for the desktop views that contain shortcuts and widgets and that can probably be removed fairly easily with a bit of hacking of the startup scripts, I'll have a look into doing that later, I'm not sure how much memory it will save over just running it with a single bare desktop though. But removing hildon-home will probably still leave the desktop "layer", which will likely need a patch to hildon-desktop to remove, which may (or may not) be beyond my abilities and probably wouldn't result in more than a negligable memory saving anyway.