The postal rate act of March 3, 1851, established the following rates for domestic mail in the United States, effective July 1, 1851: For letters of half an ounce or a single sheet traveling less than 300 miles the rate was three cents if prepaid, or five cents if not prepaid. For letters being sent more than 300 miles, the rates were six cents if prepaid and ten cents if not prepaid.
This legislation made it advantageous to use stamps because it levied a fine on letters that were not prepaid, but the use of stamps did remain optional.
When the postal rates changed, new stamps were needed. The five and ten cent 1847 issue was replaced with a one cent, a three cent, and a twelve cent stamp, each issued in 1851.
The one cent stamp met three needs:
Pre-paying the drop rate
Paying the circular/newspaper rate
Making up rates with the three cent stamp.
Essential References for your Philatelic Library, by Anonymous