Sites, like movable art, are a part of our cultural heritage. Their presence helps define the historical character of a community or nation. In every society, sites and monuments contribute to an appreciation and understanding of the past, and a sense of historical continuity.
Sites are also rich in information.
Unfortunately, this is not universally recognized. I don't think it's something that leaps out and hits the public unless it is communicated. Certainly it's something that should be communicated - the inherent information that is locked into materials and the context of the site itself. Because their environment and security are not easily controlled, sites and monuments are more vulnerable than movable cultural property. Climate, vandalism, neglect, natural disasters, and indifference all contribute to the degradation of a site.