> If you (and your team, if applicable) already know that set of languages, then there's no reason for you to learn Go.

Google is the perfect counter-example to your argument. C++, Java and Python were the 3 main programming languages in use at Google, and despite that, they designed Go and started using it instead of C++/Java/Python in some projects.

Go can be used instead of C++ when you need and can tolerate a garbage collector, and you don't need things like a custom memory allocator.

Go can be used instead of Java when you need a native executable, statically linked (like you wrote), when you need a better control over memory layout (especially to reduce pressure on the garbage collector), and when you need async IO without callbacks/promises/futures.