@nex
Because you were asking about incurring medical expenses today, and reimbursing yourself in 40 years. It sounded like you were trying to create tax-free income in retirement. That's a money losing proposition if that is the only reason you are doing it, and there are better ways to save for retirement.
If you are investing now so that you can pay future medical expenses in the future, that's what an HSA is for. And if you can afford to maximize your HSA and not seek reimbursement for small expenses today, so you can save/invest for large expenses later, that makes sense. But that's not what you asked about.
