the contact's type represents a user (buddy), but not the account's owner for which TPL_ENTITY_SELF is used
TPL_ENTITY_SELF
a named room (#TP_HANDLE_TYPE_ROOM)
the contact's type represents the owner of the account whose channel has been logged, as opposed to TPL_ENTITY_CONTACT which represents any other user
TPL_ENTITY_CONTACT
the current contact's type is unknown
the contact's type represents a user (buddy), but not the account's owner for which
TPL_ENTITY_SELFis used