If you owe money, then TurboTax will include the vouchers automatically. If you don't owe -- and don't customarily make estimated payments -- then you can just shred the vouchers. They're printed as a convenience; you aren't required to use them.
Making estimated payments is entirely up to you, though IRS & states will charge you penalties if you owe above a certain amount (based on previous year's tax liability and current year amount paid in). I don't know exactly why TurboTax will sometimes print them if you don't owe.
