I just started experimenting with @github.com Copilot in IntelliJ. First impression: surprisingly bad! “Simplify this” on JavaScript code removed 90% of the code I had just added to implement a new feature, explaining that it was complex “and not necessary for the main functionality”.

Yeah, it was just the most important part of the new functionality. On the other hand, the code really is simpler now, and I can (have to!) delete some tests too, which simplifies things even more!