In the beginning there were Library items
One of the great things about using Dreamweaver is its ability to collect together all your images and code and make it available for you to reuse throughout your site.
Library items are a great example of this, they enable you to place code/design that you will use on a number of pages into a single file, then reference it from each page.
You simply have to update the Library file and Dreamweaver will update all the pages you have placed that Library item on.
Whilst Library items bring a benefit in this respect, the fact you have to upload every page that includes the Library item following an update can be time consuming, especially when using the Library item for the Navigation, which means every page in your site has to be uploaded again.
The ideal situation would be a file, which included your design/code and was ‘linked’ to from each page, but when you updated it, you did not have to upload every page, just the one file you had worked on.