ObjDiffer's purpose is to lower the payload for the server.
You can predefine one general set of values to be shared between every user.
If a user then changes something only the changes are saved to his/her account.

Example

- Initial visit: 

var settings = new ObjDiffer(general_settings);
settings.value.on_page_item_count = 5;
var diff = settings.getDiff(); // {"on_page_item_count":5}
save_to_server(diff);

Next visits:

var patch = load_from_server();
var settings = new ObjDiffer(general_settings, patch);
alert(settings.value.on_page_item_count); // 5

See also http://tahvel.info/objdiffer/