IIRC, it's basically just that if she leaves Anki up on her Macbook without explicitly syncing & exiting, and then tries to use her iPhone or iPad, she will lose state on one of the devices.

It's a lot of cognitive overhead to remember not to touch Anki on any other devices unless you've synced and closed it out on the most recently used one.

Since she has a ton of cards, syncing takes a while. And occasionally it just throws a random error.

Moreover, there's a sense of fear every time she uses Anki that she will hit the wrong button and lose her expected state.