EasyCatalog Lite is designed for simple ‘link and update’ tasks, so the user is responsible for going through the document inserting fields where required.
The full version of EasyCatalog also offers semi-automatic pagination — for example, you can insert placeholders into library items and have them automatically populate with data. There are also more data-manipulation facilities available in the full version.
Additional modules are also available for the full version of EasyCatalog, such as the Pagination Module: this enables the automation of some kinds of publications.
There’s a list of the differences here.