I was trying to figure this out for some common code that we are putting together so I ran the following test:

function TestReferences() {
    var contextA = SP.ClientContext.get_current();
    var contextB = SP.ClientContext.get_current();

    contextA.test = 5;
    alert(contextB.test);         //Displays 5
    alert(contextA == contextB);  //Results in True
    alert(contextA === contextB); //Results in True
}

The result was that each call to SP.ClientContext.get_current() returns the same instance each time, which is what I was hoping based on the name of the function.  This is also true for the get_web() call off the client context object.  If you need to return a different context then you can still spin up your own, but if you want to reuse the same context between pieces of code then SP.ClientContext.get_current() allows you to do that without having create your own variable to share out the instance.