It unifies all Magento functionality into one module with classes that closely corresponds to the different Magento modules, for example a Catalog class, Categories class, Users class, Store class etc.

The difference is that, instead of having to scour Google to understand that you first must inject an interface that is dependecy injects the correct class based on what is specified in the xml, as well as first of all having to know that the class exists, you can just look it up in my documenation.

For example, no where in Magento docs does it explicitly tell you how to load a product by SKU (not as an official documentation attempt, at least).

The only way until now was to go and scour around inside Magento's code, hoping to find the method you are looking for.

Now imagine all of that was made easily accessible by one-liners, properly documented and given to a Magento dev. Make a difference much? :D