You are deleting the document from your computer.
In some instances this could be a file on disk. But it does not have to be.
In some instances this could be a file on disk. But it does not have to be.
The Delete button is shown, and correct, for new files that have not been saved at all yet.
Weird thing is with the setting disabled, quitting TextEdit with multiple new docs open asks if I want to "delete and quit," but Numbers only lets me "save and quit." Even if I press that, Numbers reopens those in a still-uncommitted state. So from all the CSVs I've opened in Numbers and messed with, I have literally 100 pending docs and can only get rid of them by clicking through every single one.