You can throw away the 1040-ES forms if you want. There is no requirement to file them. It's just that if you underpay your taxes during the year, the IRS has a field day as they assess penalties and fines for that.
To avoid that in the future, the next time you receive a substantial amount of income on which taxes are not withheld, you'll want to send the IRS at least 25% of that income ASAP. YOu can do that at any time you wish on line at http://www.irs.gov/directpay
