Using Content Blocks you can create one page, image, menu, or video to maintain and put it in several different places throughout your site. Examples of this might include a sub navigation, sidebar navigation, or footer. You can also use it to create templates that you may want to use throughout your site and yet maintain from one place.
Even something as simple a product or feature list. Create one content block for your list and then place it wherever you want throughout your site. If you have to makea change to the list, change it once, and the change will show up wherever you posted that particular block.