Consciousness transfer happens under various conditions. Sometimes, it replaces another person's consciousness—these are Walk-In experiences. The person/consciousness that leaves often goes to a higher vibrational existence.
Other times, consciousness transfers are shared experiences. This happens when the person receiving the shared transfer is mentally ill, such as people with Dissociative Identity Disorder. In these shared consciousness experiences, the person transferring in is a much higher vibration than the host and is there to assist them in their mission.