Well, I think the spirit is that it tries to condense into one number what normally takes two numbers. You want to know a pitcher's ERA, but if it wasn't across a lot of innings then he didn't actually contribute as much to his team as someone with a little worse ERA but 200 innings. Unless, the ERA is as bad as what you could have gotten from someone off the waiver-wire. WAR sort of does all that. But for most situations, you can tell from ERA and IP how two pitchers compare; and if it's close, other factors may play a greater role depending on what decision you are trying to make. And, as others have said, I don't see much that a pitching coach would use, by knowing it.