"There is nothing static about the SEO landscape. "[U]pdates to search algorithms can alter rankings and visibility as well as create new opportunities to help your brand stay ahead of the competition," Champion notes. For that reason, someone needs to be monitoring those changes 24/7. It's the agency's job to stay on top of developments."
Read more: http://www.marketingprofs.com/short-articles/2472/the-case-for-hiring-an-seo-agency