I prefer to have, at minimum, a dedicated data drive so that if I have to reinstall windows I don't have to rescue my data first. Not that its not backed up a bunch of times already, I'm just lazy and don't want the extra hassle of copying in several terabytes back too.
For me it's basically
SSD: OS & Apps (2TB) {recent upgrade}
SSD: A few VM's (1TB) {my old OS drive}
HDD: Data (3tb Mirrored)
HDD2: Downloads, junk, and other Misc stuff (5tb) {ok, i'm a hoarder}
