When you book a time slot with the therapist of your choice, that time slot is reserved for you. If you cancel an appointment with less than 48 hours notice, the therapist is unable to fill that time slot with an alternative client. Your therapist has to be compensated for their time, in addition to any costs they may have incurred by reserving that slot for you. For example, many therapists hire practice rooms in order to have a private and professional space from which to conduct therapy sessions.