S33 (The Notwithstanding Clause) of the Canadian Charter of Rights and Freedoms (The Charter) is a "nuclear weapon" that can be used to override the guarantees in the rest of the Charter. The original purpose and intent of it was to provide a tool that legislators could use when the conflict between the common good and individual rights was so intractable that there was no other real option other than to limit the Charter Rights of individuals in a way that exceeds the boundaries of "reasonableness" set out in S1 of the Charter.
In my lifetime, I have only seen one instance where the application of S33 has had a solid and ultimately reasonably justified application, and that is with respect to Québec's language and culture law (known at one time as Bill 101 - decades ago). The justification for that law and the use of S33 to shield it was fairly straightforward: The province of Québec exists as a unique linguistic and cultural island surrounded by an otherwise overwhelmingly anglophone cultural mosaic in the rest of North America. Therefore, it was deemed "reasonable" to allow Québec to limit the use of English and other languages within the province. Given the circumstances, I can actually agree with that reasoning even though it does place non-francophone Québecers in a more difficult situation in a number of respects. (Note: This does not mean that I agree with all of Québec's applications of S33, merely that the reasoning in this particular case made sense)