Can literally automate all the things on your Mac. Both more intuitive and more powerful than macOS' own Automator app.
Its depth and breadth place KM somewhere towards the "pro" end of the spectrum, which might (appear to) be overkill for many people.
Lets you do anything with your Mac. Automate all the things! Script apps that don't have scripting support (by replaying macros containing keypresses, mouse movements, clicks, whatever), have your Mac react to USB events, date/time, your input, device keys, external triggers, sleep/wake events, filesystem triggers, etc.
I use it heavily for a few years by now, it's one of my essential apps. New versions are usually insta-buys — when I read that v7 was released, I bought it without test-driving it first. Same thing happened a year or two later with v8. It's worth every single penny.