Difference between Dojo domClass.add() and dojo.addClass()

Dojo's official doc for addClass says

When using AMD format in a fully baseless application, add is accessed from the dojo/dom-class module.

    require(["dojo/dom-class"], function(domClass){
    // Add a class to some node:
    domClass.add("someNode", "anewClass");
});

What is meant by "fully baseless application"?

and

Alternatively, you can load dojo base in AMD style and continue using dojo.addClass in the define or require callback:

    require(["dojo"], function(dojo){
    // Add a class to some node:
    dojo.addClass("someNode", "anewClass");
});

What exactly is the difference between domClass.add() and dojo.addClass()? Why would one want to use one over the other?