The idea of appropriate use in the simplest terms is the right medication for the right patient at the right time.
Typically, for example, even now, physicians will often look at practice guidelines to decide which would be the best treatment. There is certainly the discussion—and the patient and physician relationship—but the statistics are fairly consistent that in fact a good deal of over-prescribing occurs.
For example, with seniors in particular, there are statistics showing that as many as two million seniors report that they are taking medication inappropriately. When that happens, there are often severe and serious side effects, and as a result, patients end up using health system resources, going to hospitals, etc.
“Appropriate use” is really intended to be a tool used by the physician to, as has been noted here, work towards the best possible outcome for the patient. It's another tool that would help physicians do that.