I have only ever cancelled when being sick. We did a short phone call each time in those cases. I wouldn't have been charged anything if I didn't do the call though. I think it is quite silly to charge people if they cancel, since that gives them the incentive to show up even though they are ill.

My T has mentioned multiple times that sometimes people cancel their sessions and that he might be able to fit me in if that happens. So pretty sure it happens from time to time for him. It probably also depends on the population a therapist works with. I could imagine certain types of people to cancel more often and could also see the possibility of less cancellations for example in private practice, since people usually choose to be there themselves.