The principle of pottage is considered as an evidence when the merger of adjacent lots into one larger plot that tends to produces greater land value than the sum of two sites might do separately. Plottage is known as or considered as the amount under which the value of the combined properties tend to increase if they undergo successful assemblage.
Its mostly a stylistic choice although at one points it was mostly a heat related idea. Hot air rises so having a steep roof allowed for the accumulation of hot air. It was also a good windbreaker so a collection of houses were able to stop a lot of the harsh wind from damaging things.