We know the Great Seal was an indispensable tool for keeping the government running. Historians pay close attention to the use of the Seal; not only does this help identify the time and reign of a particular warrant, but the use of lesser Seals helps us follow the movements of our itinerant kings.
Edward the Confessor is thought to have been the first English ruler to use the Great Seal, and each successive medieval monarch remade the design in his own image, to be stamped into wax. Charters, letters, and writs required a seal to initiate legally binding orders; the clerks of the Chancery wrote these orders, and the head of the Chancery was the Chancellor, usually a Bishop. So the Chancellor was officially in charge of the Great Seal and guarded it against improper use. In fact, counterfeiting the Great Seal was a serious crime, defined as High Treason in the reign of Edward III.
In official use, there were three Seals (there were many other seals—the Exchequer, Ecclesiastic Seals, Guild Seals; the list goes on and on. I am only referencing the king and his Chancery). The Great Seal was required for any state document, but if the king was traveling around, he could use a Privy Seal—first employed by King John—to move (or authenticate, or instruct) the Great Seal. Under the early Plantagenets, the Privy Seal was under the custody of the Keeper of the Wardrobe; this evolved into the Keeper of the Privy Seal. By 1312, the Barons ensured that the Privy Seal clerk was appointed by the king in Parliament and approved by them. Hence, the Privy Seal office became a sort of second clearing-house for official documents. Eventually, almost all non-judicial documents required a warrant from the Privy Seal before it could pass under the Great Seal.
Edward II, chafing at the strictures of Parliament, started using a secret seal which eventually evolved as the Signet—the king’s personal Seal—and was guarded by the king’s Secretary (precursor to the Secretary of State). In the early years, Richard II would use the Signet to move the Privy Seal, which would move the Great Seal. But in 1383, Richard got the idea that he could bypass the usual procedures, and he started using his Signet ring for everything—circumventing the Privy Seal office altogether to communicate instructions directly to the Chancery. Why did this matter? The Barons interpreted Richard’s “abuse” of the Signet as an attempt to take personal charge of government affairs, trying to shake off control of his actions. He was even recorded ordering money from the treasury for his personal use. In 1386, however, this came to a screeching halt when Parliament ordered the reorganization of his administration and impeached Michael de la Pole, his friend and his Chancellor. Richard was forced to stop issuing Signet letters “to the damage of the Realm”, and his use of the Signet fell off dramatically.