Possessing Soul Puppets allows you to take on their form during conversations (their avatar will be used in most conversations instead of yours) and grants an attribute boost to the host Soul Puppet.
The Soul Puppet attributes that are strengthened by possession will increase based on your Player Growth Attribute, Poltergeist. You can also depossess a creature with this command in camp.
Be aware of the fact that switching to another host will reduce your current spirit unless you have the Credit Shop Key Item Voodoo Pin !