KM is the most important SIG (to HRI) because HRI is built around the information structures defined by members of the SIG. There mere fact that a good information structure plus $2 will get you a cup of coffee is not important.
If you want to DO SOMETHING with that information or even DO ANYTHING AT ALL means that you really want to help people or make money or some other silly human endeavor which is find - but is you want to DO IT EFFICIENTLY or or not have to DO IT ALL BY YOURSELF - then you'll need to communicate with other people <ugh> - and if your are doing ENGINEERING or BUSINESS things - then you'll probably find SIG:PM (Project Management) helpful - but don't let them tell you they're the MOST IMPORTANT SIG - because we know that we are.