Opinions are in those jurisdictions usually published at the direction of the court, and to the extent, they contain pronouncements about what the law is and how it should be interpreted, they reinforce, change, establish, or overturn legal precedent.
[citation needed] In the majority[citation needed] of US cases, the judges issue a memorandum decision that indicates how state or federal law applies to the case and affirms or reverses the decision of the lower court.
A memorandum decision does not establish legal precedent or re-interpret the law, and cannot be invoked in subsequent cases to justify a ruling.
Several areas of commercial practice call for formal legal opinions of counsel.
Insurance policies for professional negligence will frequently require an opinion of counsel before the insurer is required to pay out on any putative claim (sometimes called a QC clause, when it must be an opinion of leading counsel).