This example shows how you can create a gangable multislider-like object. Although it is a common idea used in, for example, digital mixing consoles, there's no single object in Max yet to achieve this task of "ganging" multiple faders.
In large and complex patches that have many pattr objects, it might be useful to be able to communicate with all of them at one central location. That is the purpose of the pattrhub object. With pattrhub you can alter the contents of any pattr just by using the name of the pattr followed by the data you want to put in it.