Hold down the Option key and click on Airport or volume control to see what I mean in macOS. It gives you more information, and the information it provides is information you didn't necessarily need to have without holding down the Option key.
In airport, with the option key held, you see options to generate a wireless diagnostics report. Without the option key held, you can just switch networks. In the volume control, with the option key held, you can see options to change speaker outputs and mic inputs. Without the option key held, you just see the volume controls.
On iOS, with regular touch on the camera you get the camera. 3D touch - you get the ability to specify the camera you want before loading the app.
3D Touch is for iOS power users. Option key is for macOS power users.