These became known as Yellow backs. They were backed by gold reserves. In 1878 the government began buying huge silver reserves and mint them into dollars. Treasury Coin Notes were printed from 1890 to 1913 and were redeemable for gold and silver coin. Support the currency and provide it with inherent value.
People feel more secure about their money.
Prevents the government from printing too much money and therefore value remains high, this can also be a disadvantage. Growing economy needs a growing money supply which requires growing gold stocks. If these cannot be found then economic growth is stunted. In event of financial crisis many may convert therefore depleting national reserves. During the depression many began hoarding gold, banks began to fail and people began to cash in their dollars for gold.