Why did medieval knights carry large kite-shaped shields?

Medieval knights utilized large, kite-shaped shields primarily to provide essential body coverage when personal armour was less comprehensive.

The size of a soldier's shield is historically linked to the effectiveness of their body protection and the reach of their weapon. In the era before the development of full plate armour, knights relied on mail and other lighter defenses, necessitating a large shield to protect the body from incoming attacks. As armour technology advanced throughout the 13th and 14th centuries—eventually covering the extremities and torso with jointed plate—the knight's need for a massive shield diminished. Consequently, as personal protection became more complete and sophisticated, the large, kite-shaped shield evolved into a much smaller implement.12