Here is the part she explained that actually landed.
A budgeting app is a rear-view mirror. It connects to your accounts, waits for the money to leave, sorts it into categories, then tells you what already happened. That is useful for accounting. It is close to useless for deciding.
A sheet works the other way round. You put the month in before it happens. Rent, the car, the phone, groceries, whatever is going into savings. What is left at the bottom is not a report. It is a number you are allowed to spend.
The second half is quieter and it mattered more to me. It connects to nothing. No bank login, no third party pulling your transactions, no account to cancel. It sits on your own Google Drive and nobody else can open it.