Someone wrote the following letter to Hamodia (printed today May 2).
Kollel families receive a certain siyata dishmaya that helps them to make ends meet in a near miraculous manner. If they were to begin to keep track of their income and expenditures, they would realize that theri finances just do not add up, and the husband might feel pressured to leave kollel.
I therefore don't think it's advisable for bnei Torah to adopt Mesila's budgeting practices nor to become Mesila clients. Instead, they should have bitachon that Hashem will provide for them and not look too closely at their finances.
This attitude is a big part of the poverty problem in the Charedi world today. People are just burying their heads in the sand. I was happy to see a long answer was given, which disagrees with the premise of the question. I will just quote the conclusion:
For individuals who are on high levels of bitachon as evidenced by their modest lifestyles ... obviates the need for a budget.
But for the vast majority of Bnei Torah, budgeting is not only appropriate but required. And when perople do wat is required of them, their siyata Dishmaya is not diminished but increased.