No, that command does actually work, prefixed with "su". In fact, all of the things mentioned are still possible with su, inside adb shell, even without adbd insecure, on one of the devices this program is made for.
The thing is, say you want to pull something from a location thats "protected", you'd first have to shell into the device, "su", move it to a location accessable to adbd, logout of the shell, then adb pull. Push ? Same thing, other way around.
Same thing goes for a large number of commands, you can skip the entire "su" part needed on some devices.
Everything this enables is still possible on every rooted device, it just saves you quite a bit of typing (and hairpulling) for those who do not have adb running as root. If you use adb as much as I do, this is absolutely something you want.
On the other hand, if you're the occasional adb user only, you may not know what to do with this - and then this is not for you