Isn't this generally done anytime you don't know the structure of the json document that will be unmarshalled? If a new field is added and you're parsing to a

Isn't this generally done anytime you don't know the structure of the json document that will be unmarshalled? If a new field is added and you're parsing to a struct that struct will have to be changed to accommodate that field, rather than letting it happen anonymously as through an interface.