I use it to check does OS kernel respond to a keyboard. When kernel is dead LED wouldn't switch state. I cannot use CapsLock, because I have no, I remapped it to a compose. I cannot use ScrollLock LED, because it reflects a chosen keyboard layout, and I believe it needs more than just healthy kernel to switch LED. But I never messed with NumLock, because I see no reason.

I'd remove Insert key. I regularly hit it by accident and I see no reason for insert-mode to exist except to annoy me.