Comment by Towaway69
> Because data is fully immutable, you get a lot of nice things "for free"
This. I discovered this by implementing Flow Based Programming[1] (FBP) in Erlang[2] - the FBP is best suited to languages that are message based and immutable data structures. When using a mutable language, messages are constantly being clone as they are passed around. This does not need to be done using Erlang/BEAM.
My feeling is that FBP is a much under-rated programming paradigm and something really worth exploring as an alternative to the current programming paradigms.
My take on FBP is that data is being passed to functionality, as opposed to function being passed to data - the functional programming paradigm, or data and function is passed around as is the case with OOP.
IMHO it makes sense to pass data to functions, particularly in the times of SaaS and cloud computing.