Ask HN: Advice for working with immutable data types?

For those of you that spend a lot of time writing software based on immutable data types, what tips/tricks/advice would you give to someone journeying down this path?

FWIW, the reason I ask this is because I've been giving a lot of thought to swannodette's mori javascript library and after going through the readme, it's not super obvious how exactly to use them to simplify my life and improve my code.

http://swannodette.github.io/mori/