And the water in snow biome in expert.
By endgame you have the ability to destroy any enemy on the screen within seconds, so movement speed debuffs don't matter. Also, mounts ignore Chilled.
And you may want to use if you re-visit the underworld or want to clear a meteor.
Or you could just use a mount to float above it. Besides, Lava Waders are much better for underworld navigation in general.