What's the Point of "Replacement Player?"

Colin Wyers (BP) has a completely awesome piece today in which he reconstructs why we use Replacement Level Player, why it's better than just Average Player, redefining (and reconsidering) how Replacement Level is determined, and how BP is using that as a baseline from which to jump into WARL.*

But there's an instructive moment which Wyers really nails:

Or take the example of a player who has produced 20 runs below average. That is, again, very different if it occurs in 150 PA or 650 PA—roughly the difference between a .150 TAv and a .230 TAv.

And while above we extolled the virtues of the average player with more playing time, nobody would find a "true" .150 TAv hitter (that is to say, one who will hit .150 TAv regardless of playing time, not a hitter who hits .150 TAv over a cold streak) more valuable the more he plays—there’s an opportunity cost to deploying that hitter, in that he’s taking at-bats from a player who can do more to help his team. He’s actually hurting his team more the more he plays.

And this is why we find replacement level useful—we are trying to find the point at which a player starts to contribute to his team by playing more, as opposed to detracting from his team. And this is something that is difficult to measure, as the critics of replacement level say—but the difficulty doesn’t make it any less important for us to know.

What do you think? Is this how you would best explain it? When I first learned of VORP, I heard it described as "that value over the average player that could be called up to replace him." That holds true, but Wyer's description takes it a set further by identifying why it's important in the first place.

*Wins Above Replacement Level, BP's intended catch-all value stat.