Merchants can provide data feeds to partners of their revenue sharing programs. In addition, context oriented ads can be generated on the fly according to the page's content (so that ads can be updated more often with less effort).
Essentially, syndication provides an automated way of updating content, whether that content is an article or advertisements. Web sites become more dynamic this way, changing ads as content is updated. Publishers can send out content via RSS and XML and have it be updated in multiple places simultaneously.