What is the purpose of reworking an account? Well a good reason to rework a client site is because the search engines change the way they look at sites. If the search engine changes there methods of indexing sites then most of the site that are completed will not be compliant with the new methods. However there maybe some that do. If you don't change the content around then they will lose there placement on the search engines due to the change.

There is another reason for reworking the content of a site and that is, old content. If the spider crawls a site and indexes it and after a few times it crawls the same content is there it will lose its rankings. This because the search engine will see the site is not being update and thus less important so it will lose its ranks. So in closing if you want good rankings update your sites content often to keep up with the search engine's spider or keep the search engine from getting "bored" with the site.