What do you mean "they have more bells and whistles"? Immutable object are great because you don't need to worry about state anymore, and you are sure that your data is not changing anywhere. But.... if you need to modify the data frequently, then immutable object have very bad performance because you need to copy the whole object every time you change it. For example strings in Python are immutable, so whenever you do any operation on the string, a new string will be created.