Yeah as the other response said, side-effect free programming is great. And while it's a side effect of pure-functional programming, there's absolutely nothing that ties it to a functional approach.
"Lab toy" examples often use simplistic or unrealistic requirements to demonstrate some grand catchy abstraction. But real-world problems often end up being difficult to shoe-horn into the needed patterns. Perhaps the best and brightest can reformulate real-world requirements to fit, but they haven't codified the techniques yet. The last part seems the hardest.
