Barcoding your mail may entitle you to a lower postage price, but ONLY if all the other requirements for automation postage prices are met. A barcode alone will NOT qualify your mail for automation prices.
In general, the Postal Service recommends that, unless you are preparing a mailing for automation prices, you should NOT put barcodes on the mailpieces. As long as the mailing address is correct, your mail will still be processed efficiently without a barcode—and you won’t need to worry about having the wrong barcode on your mail. A bad (incorrect) barcode is much worse than no barcode at all. A bad barcode can cause your mailpiece to travel to the wrong destination.
What is a barcode?
Quick Service Guide 201a, Designing Letters and Cards for Automated Processing, gives an overview of barcode standards for automation-compatible letters.
Quick Service Guide 201a, Designing Flats for Automated Processing, gives an overview of barcode standards for automation-compatible flats.