It may be rare that you need to deep clone, but doing so can be a good idea nonetheless. Sometimes I want a function to not be able to mutate the original objec

It may be rare that you need to deep clone, but doing so can be a good idea nonetheless. Sometimes I want a function to not be able to mutate the original object that informs it, in which case it will receive a deep clone or return a brand new object. I find this can make complex code easier to comprehend because I can have greater confidence that return values are new and functions aren't causing side effects. Of course you can never guarantee this in JavaScript, but it's worth making a best attempt IMO.