According to RollABall tutorial, it seems that Unity will treat GameObjects without Rigidbody component as static objects, which means it may be less efficient to move them. However, even in that tutorial, it does not add Rigidbody component to the camera despite the fact that camera is moving (following the player).
So my question is: would the camera also need Rigidbody component so that Unity considers it as non-static, and would it be more efficient to do so? or is camera a special case?
I have found a discussion in the forum, but it does not address this point directly:
https://forum.unity.com/threads/does-a-moving-camera-need-a-rigidbody-attached.355583/