Why use ES6 Map?

sample.sh

$ node --harmony
> var person = { name: "Jim", age: 34 };
undefined
> var map = new Map()
undefined
> map.set(person, 'JavaScript');
undefined
> person.name = "James";
'James'
> map.get(person)
'JavaScript'
> var interests = {};
undefined
> interests[person.name] = 'JavaScript';
'JavaScript'
> person.name = "Jim";
'Jim'
> interests[person.name];
undefined
> interests["James"];
'JavaScript'
> exit