A common pitfall of frugality is to save money at the expense of your personal happiness. Example: In many companies, people head out to lunch together, grab a sandwich or whatever, eat together, and try to have a social time. That costs about $3300 a year, assuming 220 working days with the price of lunch at $15. That's a pretty large expense, and if you frame it solely in terms of food, probably not worth it for most. MMM would say that you should bring a packed lunch to work. However, I would argue that it is absolutely worth it for most office workers: chances are their jobs are in some way unpleasant, and if they bring a lunch from home, it's only a small step to eating that embarrassing, soggy PB&J in front of the screen, working and missing out on that small break. That can be very demotivating.
Beyond that, I think that some contrarian cases can be built for high-income, high-expense lifestyles. For one, an expensive lifestyle can be a great way to meet other successful people, which may open doors to opportunities. (There's a caveat on this: some kinds of expensive goodies, like vacations to Zermatt or living in a great area, are probably much better investments than buying a $15k handbag.)
Spending money on great experiences while young is also probably worth it. Having had "boring" 20s and 30s is another common regret, and it's quite feasible to prevent that, if you're confident in your earnings potential later on.