It's not just about performance, but also (perhaps primarily!) correctness: making sure that resources (not just memory) are freed in the right places, that you

It's not just about performance, but also (perhaps primarily!) correctness: making sure that resources (not just memory) are freed in the right places, that your code won't try to use resources that have already been freed, that the same object can't be mutated by two or more parties at any single point in time, etc.