You're asking this in good faith, so you don't deserve to get downvoted. I think people on hn are a bit sensitive to comments they perceive as "reductionist" that may oversimplify complex problems, even if they're honest questions.

But you're right, at it's core this kind of problem will use techniques like memoization, and most projects that need something like this will have adhoc approaches to solve this problem. The advantage of differential data flow is that it's a generalized approach to this problem. The business logic behind these workflows, between tracking dependencies and updates can get pretty damn complicated and difficult to maintain. Having a generalized approach would make building these dataflows much simpler.

The paper it's based on is pretty skimmable, so I recommend taking a look at it. https://raw.githubusercontent.com/TimelyDataflow/differentia...