The use case was for admin navigation.
In admin navigation when you develop an add-on, you can define admin navigation based on some admin permission, which get correctly exported.
However, when the user installs the add-on, the navigation for those admin permissions that belongs to non installed add-ons return true and the navigation link is displayed, I would have expected it not to display (i.e. field does not exist => false returned).
The add-on being installed is not a strict requirement so I wouldn't be putting it the addon json and you can't check those permissions with isAddOnActive or is_addon_active.
Hope it clarifies.