All-in Equity

I'm a bit confused on All-in equity. I know that it's supposed to be some kind of indication on how you're running and that it can only be measured on hands that go to showdown, but to me it seems like a worthless stat to pay attention to.
Enlighten me

AI adjusted is math adjusted green line, luck removed.

It's disliked stat because players typically only notice it when it's higher than green line

Its a statistic you can point to or look at if you ever think you are running good/bad. It can quantify something that humans have a really hard time at remembering correctly