I am in the US and perhaps that is a difference. I know it is a way for therapists to practice, and if it works for a client, then fine. In the area where I live, I have interviewed over 30 therapists (from lcsw to phds) and none of them charged for time one did not use if reasonable notice was given. They had different time periods for what they considered reasonable - usually 24 to 48 hours notice. It never concerned me that their practice would go under. I never thought it was my problem to worry about the therapist.

The therapists I see do treat it like a business but I don't pay them for time I don't use. I have been (and still am to a small extent) a solo practitioner. I charge by the hour. If a client makes an appointment and cancels, I deal with it but not by charging the client. I have court appearances cancelled, changed, and post-poned by the court or by requests from opposing counsel. It does change how much money I make that day.