There are many problems with using multiple cameras in Unity, such as having multiple audio listeners and multiple camera settings to deal with. Having a single scene camera that can be invoked from anywhere is extremely practical. It ensures that only one camera is filming and receiving audio at any time, and equalizes settings like field of view.
How will a single camera exhibit multiple movement types, like being static, following a vehicle, or any other movement that a game camera usually switches between? This is easily accomplished by attaching the camera to an object that itself has the desired movement characteristic.