When the Nats signed Matt Weiters, some questioned why. Mostly this was because they somehow missed the Nationals signing Adam Lind, despite, you know, covering baseball presumably being their job. But whatever! There was still some general truth to the statement. Weiters and Norris would be expected to hit about the same. Weiters and Norris would be expected to field about the same. Why spend more for something you already have?
Well the reason is obvious and has long been baked into negotiations. You pay for two things when you sign a player. You pay for their expected performance and you pay for the likelihood that they achieve that expected performance.
Weiters and Norris may both project to give the Nats about a 1.0 WAR. Weiters though comes off a series of seasons where he gave 0.9, 1.0 and 1.7. Norris comes off seasons of 2.6, 2.4, -0.4. Now again, these numbers should be considered rough, but in relation to the point I'm trying to make they illustrate it clearly. Weiters and Norris might have the same general expectation, but the variance in their possible performances is quite wide. A healthy Weiters might have (and I'm just throwing numbers out here) a 75% to give you a 0.5 to 1.5 WAR. Norris might have a 75% chance to give you a -0.5 to 2.5 WAR. If your goal is only to reach an expectation it may be fine to treat these two the same. However, if your goal is to avoid a terrible performance, you'd pay Weiters more than Norris. Weiters has little chance to be horrible, while Norris has a decent chance of that happening.
For a team like the Nats, who will likely be in the playoffs but want to avoid falling a few games out of home field, or the NL East, or maaaybe a few games out of the playoffs if things go poorly, that extra security is worth it.
What Weiters ensures is that the Nats have a deep line-up 1-8. Right now a good chunk of them are hitting great at the same time so everyone is overly excited about them. But what I like most is the depth. You need several bats going at the same time (unless they are super hot) to score some runs and the Nats have good coverage now. If someone is cold, if someone is injured, there are enough bats here, and on the bench, to cover that. Of course we are almost immediately asked to test this theory as someone is cold (Rendon) and someone is injured (Turner) and it worked for a couple days at least. But now Drew is injured too and we're getting into the deep bench. Presumably Turner will be back soon but right now we've hit the bottom of MI depth. It can happen that fast.
While this seems unfortunate, and it is, imagine where the Nats would be without Weiters. You'd very likely have a 6-9 hole in the lineup until Turner returns. I'm not promising the line-up will look this good all year. In fact, I'm telling you it won't. However if Werth and Zimm can produce even at average level there are no obvious holes in the line-up. With no obvious holes, they can whether the occasional storm as well as anyone. Turner and Drew out with Rendon struggling is a storm. They should be able to weather it.