Modern CMSs allow pages to be added and edited with a simple interface that resembles a word processor, such as Microsoft Word. They do not require the user to have any technical web design knowledge - updating site content with a CMS can be done by anyone with competent word processing skills.
CMSs keep the style and layout of pages identical, and are also able to automatically update menus and other navigational aids. Therefore, adding and updating pages only requires you to concentrate on the content - the formatting, layout and menus are handled automatically, and a consistent appearance across the entire site is guaranteed. This is particularly valuable if you have multiple people updating your site content.
A good CMS will also allow you to make changes from an ordinary web browser, meaning that you do not have to purchase extra, expensive software just to keep your site up-to-date.
Since CMSs can be used to make changes at any time, by anyone, content can be kept up-to-date with minimal cost and minimal fuss.
Specialised training is virtually eliminated; adding and updating pages is intuitive. CMS interfaces often resemble common word processors. For small businesses, this ability to use a system without special training is critical. Training up a staff member in complex and cumbersome systems such as Microsoft FrontPage or Adobe ColdFusion is expensive and can be a complete loss if the staff member leaves - taking the training with them. All of this is avoided with a good easy-to-use CMS.