Points. I'd like to keep my slann under the 400 mark with bsb. Although I might shift that to the scar vet witg more miscast chance.
Coming from a playgroup where 500+ point Vampire Lords, Daemon Princes, and Greater Daemons are commonplace, I have to say that keeping a Lord's points cost under a certain level isn't a thing I usually consider to be a priority. I mean, what do the points that you save by not including Soul of Stone really get you?