Do I need to create an "Empty" Layer for objects that will not have a collider?

Questions & Answers
1

So, all objects have Layers, regardless of having a Collider or not.

Let’s say I have an object that will only hold a script, and will not have any colliders or rigidbodies. It will have the “Default” layer set (and that layer is used for many purposes, specially for collisions)

Even without a collider, will that affect performance in any way, or do I need to create an “Empty” Layer, and in the Physics settings untick all boxes in the Layer Matrix?

2

If your objects don’t have a collider or rigidbody, you don’t need to worry about layers, since the Physics Engine will not take them into consideration as @TreyH also points out.

But on the other hand, if they do have a collider, then you can use layers, and the “Layer Collision Matrix” in the Physics Manager, to define if each layer will interact with other layers.