Dividing Lines

The U.S.' and Canada's states are often divided by a straight line according to latitude and longitude.

This way of dividing region is a very new system, so you never see this kind of straight lines in old countries. The old way (or much common way) of dividing regions is to set the borderline according to the land features, such as rivers or mountains.

Since latitude and longitude are not visible, dividing by the land features seems more understandable. However, it may cause more conflict between the two regions since the land area is usually not equal. (Also, the land features can be changed by some natural forces such as flood and eruption, or by the human power.)

So, which is the more useful way of dividing?
... I don't know.