Nearly every heraldry site you see will state that coats of arms (family crests to some) were invented so that one could tell one mounted rider from another in battle. The heraldic scholar, A.C. Fox-Davies points out that coats of arms were in existence long before the closed helmet was invented, and were probably more to do with vanity than anything else.
Up until 1944 in England, if your family had a hereditary grant of a coat of arms, you were required to pay a levy of two guineas (A guinea was one pound, and one shilling) per year to the Inland Revenue. This tax of about $4 per coat of arms raised more than $100,000 per year.
The use of an actual “coat of arms” i.e. a surcoat emblazoned with the wearer’s coat of arms was a product of the Crusades. The surcoat and lambrequin were worn over the suit of armor and protected the knight from the intense sun of the Middle East. The suit was also given some protection from rust.
The Court Of Chivalry dealt with cases brought before it where one man would have insulted another, perhaps by calling him “A base and lying fellow” ( An actual case brought by one A. Baker in 1637) The inference being that the chap was not a gentleman. The usual winning argument was that if a man held a grant of a coat of arms, he was, by definition, a gentleman.
The Beefeaters, those finely turned-out guards at The Tower of London, wear the scarlet uniform embroidered with the badge of the Sovereign of the day. The basic design of the uniform is exactly the same today as it was in the reign of Henry VIII.