Every SharePoint project starts off well-structured and everyone knows where to find the information they need. As time goes by, however, more and more sites are created – including some that are only relevant for a short period of time and are soon forgotten. After a while, your SharePoint environment becomes cluttered with irrelevant sites and people can't find what they're looking for any more.
We've seen this problem several times already and refer to it as "site chaos". We recommend acting as soon as possible, because in this case, prevention definitely is better than cure.