Using bit shifting allows you to take into account multiple layers in one physics operation:
Physics.Raycast(ray, out hitInfo, Mathf.Infinity, layerMask ) Without bit shifting, you would be allowed to raycast in one layer and only one. While with bit shifting, you can raycast in multiple specific layers:
layerMask = (1 << LayerMask.NameToLayer("MyLayer1")) | (1 << LayerMask.NameToLayer("MyLayer2")) ; You can also raycast in every layers except specific ones :
layerMask = (1 << LayerMask.NameToLayer("MyLayer1")) | (1 << LayerMask.NameToLayer("MyLayer2")) ; layerMask = ~layerMask; If you look at the "Layer manager" in Unity, layers can be seen as the indices of a simple one-dimension array.
EDIT : I've never seen it before, but the LayerMask class has a utility function to get the "computed" layer mask given the layers names :
Debug.Log( LayerMask.GetMask("UserLayerA", "UserLayerB") ) ; Suppose UserLayerA and UserLayerB are the tenth and eleventh layers. These will have a User Layer values of 10 and 11. To obtain their layer mask value their names can be passed into GetMask. The argument can either be a list of their names or an array of strings storing their names. In this case the return value will be 2^10 + 2^11 = 3072.
Link to documentation : https://docs.unity3d.com/ScriptReference/LayerMask.GetMask.html
