No, I don't think POSIX is as necessary as many people make it out to be, because it really depends on your use case. I've always been able to rely on bash both

No, I don't think POSIX is as necessary as many people make it out to be, because it really depends on your use case. I've always been able to rely on bash both professionally and in my own projects. I am however aware of people who have to rely on posix compatibility. One of them is as you said, docker environments and alpine Linux, the other is a former colleague was working on some airgapped system where security didn't allow any additional packages to be installed, and bash wasn't installed. So their only way of scripting was either posix, or an old version of python 2 (I think it was 2.3). I don't know whose brilliant idea it was to install python, but not bash. So it really depends on your use case