The problem with spending money -- and consumption in general -- is the opportunity cost. If by doing something you are not maximizing some value, then it would be better if you did.

The same criticism could be also made about production: if you work hard and make profit by creating value, but by doing something else you could create even more value, then it would be better if you did the other thing.

Perhaps the difference is that on the production side people at least try to maximize (of course with all the human irrationality involved), but on the consumption side we often forget to think about it. So we need to be reminded there more.