Having just read a Clin Lab News article on QC which IMHO is misleading, here are my thoughts.
The purpose of QC is to determine whether a process is in control or not. In clinical chemistry, the process is running an assay. An out of control process is undesirable because it can yield unpredictable results.
QC by itself cannot guarantee the quality of patient results, even when the process is in control. This is because QC does not detect all errors (example an interference).
The quality of the results of an in control process is called the process capability of the process (e.g., its inherent accuracy). QC cannot change this, regardless of the QC rules that are used.
QC is like insurance, hence cost should not be considered in designing a QC program. That is, regardless of how low risk a failure mode is, one should never abandon QC.
Although running more QC can detect an out of control process sooner, any QC program should always protect patient results from being reported when an out of control condition is detected. Risk is not involved.