The Wizards may also receive cash in the deal, and they probably won't be sending any players back to the Knicks (so who knows exactly what Washington is giving up).
Turiaf, who turns 29 in January, has averaged 5.3 points and 3.8 rebounds per game in six NBA seasons. He's also averaged 1.5 assists and 1.4 blocks per game. Turiaf is not much of a scorer; he's more of a hustle/high-energy guy who will rebound and play defense. So, he presents something off the bench that the Wizards haven't had much of for a while.
That doesn't mean he's a great player (he's not) or that he's going to see huge minutes (he shouldn't, especially if that means cutting into the minutes of Booker and Singleton). But since he'll defend and rebound, he may end up replacing McGee and Blatche more than a few times during this lockout-shortened season. And considering how compact this season will be, it's not a bad idea to have lots of depth.
Another positive: Turiaf will make a little over $4 million this season ($4.36 million according to ShamSports), but he's also in the last year of his deal. And since the Wizards still need to spend some money to reach the new salary cap floor, it's not a bad idea to acquire someone in the last year of his contract. If you subscribe to the sort of theory that a guy in the last year of his contract plays harder so that he sets himself up with a new deal afterwards, well, then that's another bonus of this trade. Regardless, it makes sense.
One more thing: Turiaf tends to get a little animated during games, so hopefully he provides a few of these moments for the Wizards: