Primary use case is privacy. Just like "right to be forgotten" in Europe, as part of GDPR, which is a law on the books. Blockchains cannot forget, and everything is traced, so the only way to be forgotten on chain is via a mixer of some sort.
That's my right as a sovereign, free man, to decide how I do my business. And it's not for you or anyone else to decide what math or algorithms I use to achieve that.
Just chiming in to say that GDPR doesn’t apply to financial data. Financial companies are obligated to keep you data for a long period of time and is a case where GDPR requests do not apply.