Here is a link that explains just how important it was to bear and display the correct arms. Just think of the Battle of Barnet, when in the fog the Earl of Oxford’s “star with rays” was mistaken for Edward IV’s “sun in splendour”, leading two allies to turn upon each other. Needless to say, Edward emerged the victor.
When there was a dispute about who had the right to bear particular arms, it was heard before the Court of Chivalry, and one of the most celebrated of such cases was that between the Scrope and Grovensor families, which occurred during the reign of Richard II and saw evidence given by a huge portion of the aristocracy. Some had important evidence to give, others had little to add, but they all turned up. It was a matter of immense importance to them all that specific arms were borne by specific men. Any confusion, and another Battle of Barnet situation could and probably would arise. One needed to know and be certain of who was friend and who was foe.
To read more about the Scrope and Grosvenor dispute, I recommend the following book, which goes into great detail about who said what. Very interesting indeed. An insight into the world of late-14th-century society and chivalry.
The title of this book may suggest it is all in Latin, but it isn’t. Although there are passages in Latin and medieval French, the book is mainly in English.