Complex event/stream processing vendors compete fiercely on the basis of low latency, down to the single-digit number of milliseconds, or even sub-millisecond levels. A question naturally springs to mind: When does this extreme low latency matter?
I think I’ve come up with a concise yet fairly accurate answer: Super-low latency matters when the application includes direct competition against a similarly fast opponent. The best example is automated stock trading – if you can exploit a market inefficiency 1 millisecond before your competition, you make money.
Other examples might arise in network security or battlefield systems, but I don’t know of any specific real-life cases. Instead, other applications for complex event/stream processing tend to be content with latencies that are easier to achieve. E.g., 100 milliseconds (1/10 of second) is likely to be plenty fast enough.