However, that ship has sailed - the Mets did not acquire that great platoon partner. As with any good opportunity which is missed, it is time to re-evaluate and move on. At this point, there is almost no benefit to platooning Daniel Murphy, and the Mets would be better off playing him every day.
Metsblog linked to a pretty good article today over at Exile on 126th Street, where the author concluded that:
Fernando Tatis is the Mets' best bet against lefties, if you don't want to adjust for age - and you might not want to with someone like Tatis. He posted a .797 OPS against lefties in 2009, and there's no reason he can't do it again. Some players maintain their offensive abilities with age, and Tatis appears to be one of them, putting up two solid offensive years at age 33 and 34.The reasoning is sound, but I disagree with the conclusion.
A Tatis/Murphy platoon works best at first. They're both average hitters, plus-defenders, and Tatis is viable at multiple positions, adding to his value on the bench.
The difference between Fernando Tatis and Daniel Murphy against lefthanded pitching is negligible. As the article points out, Daniel Murphy's career OPS thus far against lefties is a paltry 732 compared to Fernando Tatis' career 797 OPS. Adjusting for age, the gap practically disappears.
However, even if you weren't going to adjust much for age, and to assume that Fernando will be about 50 points better than Murphy against lefties, what benefit does that even provide? 20 points of on-base percengate and 30 points of slugging? That would be the equivalent of one extra hit or walk per every FIFTY at-bats.
At that point, it makes more sense to just go with Murphy full time and see what he can do for us. Since the Mets seem committed to the Murphy experiment for at least 2010, it is far more beneficial for us to give him a chance.
Add in the fact that Murphy, according to the metrics, is superior to Tatis on defense, and you have the very serious chance that Murphy might be a better option against lefties than Tatis is, outright.
I was all in favor of platooning Murphy when there appeared to be an opportunity to acquire a player who could be a legitimate strength against left-handed pitching. Fernando Tatis is not that player. I'd prefer that the Mets give Murphy the chance to succeed and have Tatis reprise his role as super-sub.
 From the Garko article:
I think we have the roster space and the need for a guy like Garko...As for the platoon itself, Garko has had 422 at bats against lefties in his career and his batting line is .313/.392/.495. Murphy has only 104 at bats against lefties but has only hit .240/.289/.442 against them. However, Murphy even in the minors had a big split - a 832 OPS versus righties and a 725 OPS versus lefties.
Combining Murphy and Garko's platoon splits would give us a first baseman with an OPS above 800. Put another way, that is the difference between Yadier Molina and ... Adam LaRoche (844 OPS).
In addition, we'd have an opposite handed pinch hitter for late in the game if we needed someone to avoid a specialist. The Mets have missed having a big pinch hitter late in games for years - it would be nice to finally have one.
 And for what its worth, Tatis actually posted an 822 OPS against lefties last season. He also has an 808 OPS against lefties for his career, so I am not sure where those numbers came from.
 It is finally nice to see Tatis getting some props around the blogosphere for his performance the last couple years. It has been a real underrated real asset to the Mets to have a pleasant, workmanlike player who is willing to be a backup and can competently play four defensive positions. It has been a pleasure to have him so cheaply.