Its useless imo. There is a thread about it on this forum , people arguing that it helps alot, but I bet those same people are the ones that spent the actual time leveling it and to hard headed to give up their stance. Their argument is "every little bit helps". On that thread, I think I calculated out the % it helps theoretically.
Only way that is worth doing is if you afk bot it to max, spending any time on it is just dumb, you are better served with a 10-20 ac upgrade from an item.