Immutable Architecture - What Are the Primary Benefits?

The primary benefit that i've found is that now you can really reason about your systems. You can understand what they're going to do, which, when your talkin about a distributed system, that hus really been almost impossible to do. So the kinds of systems that you can build once you've adopted this are progressive web aps where you've got your state on the mole defice and things can go off line and the user can still work with the system.