If the entity's current model has no physics mesh associated to it, no physics object will be created and the previous object will still exist, if applicable.
Clientside physics objects are broken and do not move properly in some cases. Physics objects should only created on the server or you will experience incorrect physgun beam position, prediction issues, and other unexpected behavior.
The solid type of the physics object to create, see SOLID_ Enums. Should be SOLID_VPHYSICS in most cases.
Using SOLID_NONE will only delete the current physics object - it does not create a new one.