It compares the item with the target state, the open planning items, the Rules of Staging and Production and the principles and rules agents keep in the project's manifest, and a plan that would break a rule counts as a conflict. A similar check runs when you save a rule.
If the item is new, it is saved at once and you see nothing of the check. If it looks like a duplicate or a conflict, the window shows the items it repeats or conflicts with and why, and the button becomes Save anyway: change the item, or keep it as it is. Changing any field cancels Save anyway, so the check runs again on the new text.
If the AI check cannot answer, for example because AI is not configured on the SyncNow server, the item is saved without it: the check is advice, not a gate. Anything that looks like a password or key is removed from the text before it leaves the SyncNow server.