[Taqwus]

...ex. if you're playing the Dreamlands with high dominion, you'll acquire hordes of really, really lousy freespawn that still eat as much as far more useful troops.

Of course, since they're freespawn, you might not actually care that they starve -- but if you have real troops backing them up, you may want enough supply because you can't guarantee that it'll be the freespawn who starve twice in a row and get diseased.

And also where you are, of course. Wandering through the former territory of the Ashen Empire, you'll still want supply items.