Any EPUB in the hundreds of MB. I am aware of the use of a temp folder.
. I was just thinking perhaps - if it is a good idea, I don’t know - updating the EPUB in place with only changes, at times when possible. Or keeping a saved working copy that is updated as such and then replaces original.
Some of us, I’m not sure how many, are more comfortable with somewhat frequent saves.
Whether problematic in some cases, unsure. But would be nice someday if it can be done. If for example, at relevant times on disk EPUB file structure was stored and compared when saving.