There are at least a couple major problems with this method. First, it's pretty easy to overlook quite a few expenses. Things like that daily stop at the coffee shop, or the cost of a car registration that happens only once a year.
In a budget template, you will list down all the accounts that you have and this will surely allow you to have more savings. The chances of getting debts is actually very small since you can easily check the exact money that you still have to make it work for your expenses.