[athenot]

That was a point I remembered from Apple's Human Interface guidelines. From the 1987 edition, on modal dialog boxes:

Because it restricts the user's freedom of action, you should use this type of dialog box sparingly. In particular, the user can't choose a menu item while a modal dialog box is up and therefore can do only the simplest kinds of text editing. For these reasons, the main use of a modal dialog box is when it's important for the user to complete an operation before doing anything else.

Source: https://andymatuschak.org/files/papers/Apple%20Human%20Inter... p.59