How much energy can you save by adding exterior shading? What would be the return on investment on a better window? How about adding a shaded patio? Wouldn’t it get too dark inside? The only way to find out is to simulate these alternatives ahead of time, because the same component would perform differently in different buildings.
These analysis are performed for identififcation of comparative energy impact of individual components of a building. Also helpful in design of passive energy houses, taking advantage of passive solar heat.