Idk, I've gotten so used to avoid using starfall on anything but a boss, I won't pop it any other time. Really the only fight I'm happy to press it is on Magmaw /w the adds. Otherwise I'm scared to pull everything and have to listen to my GM rage.
I tested it once on trash in Grim Batol and it didn't hit any mobs, except their pets and we got wtfpwnd.