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.
Of course, when it comes to picking out the type and design of worksheet you would want for you and your family to use, always consider your needs. Just because availing of a free worksheet will be more practical for you now does not mean that your finance management plans will be better off. But also, budgeting worksheets are not enough if you want to succeed with budgeting, you must have the right mindset too.