if someone writes down all expenses in the budget appendix and knows all their expenses, then that's great. Because two or three months of such records are enough and all expenses will become obvious. And after that, it will be possible to forecast expenses for the month, know how much money will be needed. And if such a guy knows how much money he earns and how much he spends, then he can understand how much free money he has left per month. And then you can invest this money without fear of spending extra money that could be needed for everyday needs.
That is great, ONLY if you can remove some of the expenses and can do better. I check every month, and for the past 3 years or so, 80% of the big spending that I did was for "unexpected" stuff, medical bills (how could I know ı would get sick), friends getting married (you gotta get them a present and go to some place), business related, unexpected taxes, some fine I had to pay, washing machine broke down, tv broke down, wife got sick this time, and many stuff like that basically. None of them are my normal month to month expense.
That is why we can't really consider budgeting as valid way to move, because it doesn't work the way you hope it would work. If you could do a better job, then you won't be needing the budget, because you can't spend any less than you could, if you could, you would, what you need (or all of us need) is more income.