Exorcism can easily become psychologically damaging as the procedure is likely to be stressful for the person who is believed to be possessed. One example in Texas involved holding a 17-year old down and screaming for hours. Exorcism tends to be done to people, often children who are vulnerable because of physical or psychological illness.
Exorcism can be done because someone is sick or simply because someone goes against the leaders of a church group of goes against the group teachings. Exorcism can therefore be an effective way of controlling wayward church members or members who can see that the church is teaching unreasonably stuff.