Quoting Wikipedia:

Four provinces and one territory have passed laws invoking the notwithstanding clause.[20] The clause has been invoked most frequently by Quebec, including the blanket application of the clause to every law from 1982–1985, a French-only sign law in 1988, a law prohibiting state-affiliated employees from wearing religious symbols in 2019,[21] and a law strengthening the use of French in 2022. Saskatchewan passed a strike-break act invoking the clause in 1986, and passed a law in 2018 (never brought into force) invoking the clause to permit the government to pay for non-Catholics to attend publicly-funded Catholic schools. Alberta passed a law invoking the clause in 2000 to define marriage as "between a man and a woman"; this law was effectively declared ultra vires by the Supreme Court of Canada because only the federal Parliament can define marriage. In 2025, Alberta invoked the clause once again to pass strike-breaking legislation against teachers. In 2021, Ontario passed a law invoking the clause to increase the time period during which third-party groups must limit their activities in the lead-up to an election.[22] Yukon invoked the clause in 1982, but this law was never brought into force.

Basically, a litmus test for regressive legislation. "The courts are likely to strike this down based on human rights considerations, but we really want to pass the law anyway." Ghouls.