Like Captain Nippon said, it seems lazy. But because of the unit size increments, you'll be left with 2 unusable Horrors or Flayers if you build a Courtier Hero out of the box. You can try to build 3 Courtiers out of one box, using all the models, but the Courtiers use the "champion" bits and there wouldn't be enough in one box to appropriately kit out all three.
Probably not much of an issue if you have a large enough collection; If you've combined two boxes into a 6-man unit, you'll have a spare set of champion bits, or you could eventually add up the spare models into a full unit increment.
The Crypt Ghast Courtier is a little more egregious though, because it leaves you with NINE spare ghouls. (I guess you could pay points for 10 and field them one short, but still.)