This gleam indicates that there's new content at the site. A notification channel simply tells the client that new content is available. The user can also opt to have email sent when new content is posted. Sitemaps can be used to pass information about a hierarchy of related pages, which can be used for navigation within the Channel Bar. These first two types are often combined to notify the client of new content and offer a preview of what's waiting.
Clients can also opt to download all new content.
That's where offline content caching comes in. The CDF lets you schedule updates of your content to client machines while minimizing loads on the server. Another cool feature is that you can collect page-hit information from offline users just as you currently do with online visitors. As the client views the offline pages, a local log file is created. That log file is uploaded to a specified directory on your server the next time the client updates the channel.