Our family is two W2s which don't qualify FA. Someone suggested us to fill the form. The rational is to show the school: You have decent income and your kid won't potentally quit in the future due to any financial reasons. In short, it said filling the form helps the application even you don't want FA or even merit scholorship (for T5).
In the end, we didn't fill and we are lucky that kid is admitted in an EA top school. So who knows which way is the better one.