The description of the Amulet of the Black Skull from Tomb of Annihilation says, in part:
[...] You can use an action to expend 1 of its charges to transport yourself and anything you are wearing or carrying to a location within 100 feet of you. The destination you choose doesn’t need to be in your line of sight, but it must be familiar to you (in other words, a place you have seen or visited), and it must be on the same plane of existence as you.
Since the item description already specifies that the location must be "within 100 feet of you", saying that the location "must be on the same plane of existence as you" seems redundant.
Are there any situations when this is definitively not a redundancy?
I’ve never played Tomb of Annihilation; is there an adventure-specific circumstance I’m not aware of that makes it necessary to specify both restrictions in the description of the item?