First, in Reagent/FRP, I was updating a view based on the value of an atom. This meant I had different default values in different atoms. The big atom let me unify where I stored values, and reuse values, without a performance hit. Second, the big atom made storing application state trivial: you can just throw the map/record in Redis or something.

However, the big atom is just a big map, and keys can be paired with any value, so it is not enforcing types. From a Haskell perspective (where I understand the program almost falls out of the types you define!), this probably does increase the scope for error.

This can be mitigated with Schema (which I never used effectively), logging changes to the console, and being able to see your default map easily (like, there's a map in one file which I load upfront, so I can see what values are there).

I'd welcome hearing from anyone with a more advanced or precise use of re-frame state.