If you can be confident that you can coast your whole life and be well-off, then I have no argument against it.
If you are not confident, or perhaps want to make sure your children have a work ethic that is more likely to give them a good life - then it's a big risk to assume you can chill and all will be fine.
The OP isn't coasting, it's about not maximizing productivity for the sake of it. It's about striking the right balance, avoiding burnout, working smarter not harder. Too often productivity becomes a cargo cult of austere asceticism rather than something that actually enriches one's life. Some days it's okay to work-to-rule.
If you are not confident, or perhaps want to make sure your children have a work ethic that is more likely to give them a good life - then it's a big risk to assume you can chill and all will be fine.