(Responding from the perspective of Materialize, the technology and company built on top of Differential Dataflow) Some examples we're seeing interest for:

Building realtime, low-latency (< 10 sec) dashboards. The type of things where you previously would have had to wait for several hours or a day for ETL pipelines to crunch through a lot of numbers.

We're also fielding interest for streaming ML applications. Ie, moving from batch models to streaming models.

Also worth pointing out that Differential Dataflow has been around for awhile, while Materialize is fairly young. We're still constantly learning about new applications!

This is useful for financial simulations. Used it to backtest trading strategies on billions of stock quotes in microseconds, about 20 years ago.