The original need of a flag to be distinguishable and stand out at a distance was mainly driven by military necessity. At sea ships needed to be able to identify themselves from a distance, and on land armies face the same necessity. Quite frankly they needed to know who to shoot at and who not to.
This said, distinguishing one flag from another has led to many changes in the theory of flag design and this modern trend to a more abstract-looking flag has been one of the results. Also, in recent years one has seen an increased interest in flag designs, with contests at both state and local level resulting in new designs.
Ted Kaye’s small pamphlet Good Flag, Bad Flag has become one of the driving forces behind this phenomena and interest in flag design. It has had a profound and sometimes controversial effect on the traditional concepts of flag design.