It's polite to cancel an appointment that you can't make.
Frank is due to see his doctor this afternoon, but he feels better now.
Frank wants to decide what to do.
Frank calls up to inform the doctors office he won't be coming in.
Frank decides not to see his doctor but doesn't call to inform the office.
The doctor is able to fit someone in Franks place, so they can get medical attention.
The doctor wastes time that could have been spent helping someone who needed help.