Content Deployment - Best Practices

 Full content deployment is done only on empty site collection, if we want to deploy the content only for the modifiled pages, content  then we go with incremental deployment.

Content deployment copies content from a source Microsoft Office SharePoint Server 2007 site collection to a destination site collection. The entire source site collection can be copied (full), or a subset of sites can be copied (incremental). In either case, content deployment is incremental by default, deploying only changed pages and related assets (such as images). You can also do a full deployment of all content; however, you should only run a full deployment job on an empty site collection. Also, a Quick Deploy feature supports deployment of a single page by authors

http://blogs.technet.com/b/stefan_gossner/archive/2009/01/16/content-deployment-best-practices.aspx