What is mootness and what is the effect of mootness?

The doctrine of mootness and its proper application were explained in Borowski v. Canada (Attorney General), 1989 CanLII 123 (SCC), [1989] 1 S.C.R. 342. As noted at 353, courts will generally decline to hear cases which raise merely hypothetical or abstract questions, but retain a discretion to depart from that practice if it is warranted by the circumstances: The doctrine of mootness is an aspect of a general policy or practice that a court may decline to decide a case which raises merely a hypothetical or abstract question. The general principle applies when the decision of the court will not have the effect of resolving some controversy which affects or may affect the rights of the parties. If the decision of the court will have no practical effect on such rights, the court will decline to decide the case. This essential ingredient must be present not only when the action or proceeding is commenced but at the time when the court is called upon to reach a decision. Accordingly if, subsequent to the initiation of the action or proceeding, events occur which affect the relationship of the parties so that no present live controversy exists which affects the rights of the parties, the case is said to be moot. The general policy or practice is enforced in moot cases unless the court exercises its discretion to depart from its policy or practice.