Do I need a CMS?

You probably will need a CMS if the following are TRUE:

Does your business and the services/products that it offers change often? Does your site need to be current?
How many people are involved in updating your web site?
Does you current site have a consistent look throughout? Are some pages 'broken'?
Is there someone on staff who could assume the additional responsibilities of maintaining your site?
Would your business benefit from maintaining archives of past data for your web site & syndicating its content?
You should revisit this regularly at least quarterly and whenever you add additional functionality or content areas.

You have a small organisation where web publishing is in-house, and can communicate exceptionally well with content providers & producers
Your site is small and doesn't update frequently in content or structure
Your online operation doesn't perform any personalisation
You don't integrate content between the web site and retail outlets, call centres, email newsletters or other channels
You don't need to manage specifications from Retail & Development to customer support
You are not offering customers a community where they can contribute to a site
One individual has intimate knowledge of the entire site (and others have intimate knowledge over their own sections)