A camera on the outside of the door is only useful if someone can see the image. That is the whole argument for an indoor screen.
The intercom problem
An app notification works when the phone is in your hand and the network is up. A screen works when you are walking past the door with wet hands.
What the screen shows
The cat-eye view, the visitor, the unlock state and the battery level. On the F39HR the rear panel is a 4.0″ IPS display; the front is a 0.96″ OLED for status only.
When it is overkill
Interior doors, secondary entrances and projects where the building already has a video intercom. Do not pay for a screen the door will never use.
Takeaway
A screen is a convenience for the person inside, not a feature for the datasheet.