New patients are often surprised that I do not favor sessions every other week. There is a very good reason for the norm of at least weekly sessions in therapy. I think of it in terms of therapeutic dosage. In a depth or psychodynamic approach, the relationship between the therapist and the patient and the feelings and fantasies and thoughts the patient has are a critical pieces of the therapy. When sessions are spread out too far, the work too easily becomes intellectual and does not really touch anything of immediate and emotional importance. There is too little contact with therapist for the therapy to move beyond a business transaction or a helpful advice session.
In classical psychoanalysis, patient have sessions 3-5 times per week. Not many people have the time or money available for that kind of intensity. And of course for those relying on health insurance to cover therapy, that kind of treatment is almost never approved. So the norm has become once a week. And that does seem to be the basic minimum for depth work.
People who have been in therapy for quite a while and comfortable with the way it works and what it requires may be able to move to every other week and still do significant work. But for the most part, for the duration of therapy, best practice suggests that once a week is a workable minimum.