There are likely as many answers to this question as there are people keeping spirits. Spirit Keepers do so for their own personal reasons. One very common reason is companionship. Additionally, many do so in their quest to gain knowledge of different realms, worlds, and time periods. Spirits also guide and help people in enhancement of their natural abilities, as well as developing supernatural abilities. Through spirit companions, many people discover various disciplines of magick, support with spell castings, and other aspects of guidance in paranormal endeavors. Many folk just naturally feel drawn to being around spirits and welcoming them as companions. Spirit Keeping offers a unique and mutually beneficial relationship to both spirit and Keeper.
The practice of this branch of the paranormal is based strongly on Spiritualism, and should be not confused with being religious. Those who practice Spirit Keeping may or may not subscribe to a particular religion.