[pier25]

Nothing IMO but a lot of folks argue that using immutable state and functional paradigm results in more predictable applications.

Not sure if all this immutability talk in the JS community is parroting because "it's what Facebooks does" or what. Maybe it makes sense once you are building really big front end projects but personally I've never had an issue with mutable state in small to medium sized projects (less than 50k LOCs). Although I admit I've never worked on a Facebook-scale kind of project.