For a variety of underlying psychological and sociological reasons, some consumers may feel better about their purchase if it is perceived to be 'good' for the planet.
Of course, whether it is actually good or not may be another factor, and sometimes peer-group pressure may be at variance with the technical reality.
As an example, the Independent newspaper reported in 2007 a case, probably not an isolated one, of a London house owner who had installed a solar panel on the north side of their house.
Technically, the panel would be useless, because of the lack of direct sunlight, but for the house owner, the north side of the house could be seen by everybody.
A panel on the south side of the house would not be visible, and would be less able therefore to make a statement about their 'green' credentials.