How Quartered Designs on Various Coat of Arms Came to Be

Quartered designs, that people imitate so often, come not from single time intentional design, but from mergers and such.

Two individual places had a simple flag each that followed rules of tincture and such. Then they merged and now symbols of each had to be displayed together so that everyone knows this is an army or person of united kingdoms, duchies or counties.

More ordinary personal example of this approach is hyphenated family. Both surnames were considered important enough to create new hyphenated one. Family of Johnsons merged with Morrisons. Their descendants were hence known as Johnsons-Morrisons

One well documented example is the UK. England used to have a simple red cross on white. Scotland simple white saltire (x-cross) on blue. However when Scotland and England united into United Kingdom, each place wished for their symbol to be on the united flag. At first they simply depicted them side by side, like in this article.

In the UK they eventually came up with more aesthetically pleasing version of the flag. Now iconic Union Jack. In many other places the resign remained as hyphenated as before. Some times adding more and more mergers.

The worst example would be Coat of Arms to two Sicilies. The bearer of this basically claims to be a descendant of everyone under the sun. Almost like John James Washington-Lincoln-Roosevelt-Reagan-Bush-Clinton-Trump-Obama-Stalin-Tsedong-Genghis-Temur-Ceasar-Moses. 

Notice a presence of golden cross on white, the symbol of Crusader era Kingdom of Jerusalem. Rulers of Two Sicilies unironically claimed to be Kings of Jerusalem as well many other places all over the Europe.