The only question is, can you express some of the state-relations as serial code? If "relationships became intricate (a computation graph)", chances are, you shouldn't use serial code anymore, because that splits dependencies in a two-class society: those that are expressed using code and those that are expressed using dead data. It is usually preferable to specify everything as dead data if the relationships get complex, and to then code sort of a virtual machine that "executes" the data.
So it's in fact the simple cases that lend themselves to being expressed as serial code. I won't argue with that there are nice looking example usages. Problem is, as always, systems that help making the simple things easy often make the hard things impossible.
