The best practical understanding of Petricek's work I gained from using Clojurescript's Re-frame library. In re-frame, coeffects represent the data that an event handler needs from the outside world to do its job (like current time, random numbers, or local storage values). This aligns with the academic concept of tracking contextual dependencies, just applied practically in a front-end framework context.

The main difference is that re-frame uses a more pragmatic, simplified version focused specifically on event handling in web applications, rather than the full mathematical formalism of the academic work.

Learning re-frame was a light-bulb moment for me. I highly recommend giving it a try, even if there's never a plan to use Clojure or Clojurescript in practice.