Estimated tax for 2017 why I hace to calculate?

Me & my husband are employee of company and NJ tax due is about 1000 dollar & we were brought to NJ Estimated Tax for 2017 screen from TurboTax. We don't know why we have to do NJ Estimated Tax for 2017. Should we change withholding to Single for State, we do not worry to do estimated tax for 2017? Even we pay less, we will do Tax return for 2017 next year & pay due, why we must worry Estimated Tax & penalty from IRS?