Last year, the Rockets had no defense for their lack of defense.
Per Hoopdata.com, they were 28th in the league in opponents points scored per game, 23rd in defensive plays rate (measuring the combination of blocks, steals and charges they caused as a team) and 18th in opponents' true shooting percentage.
The addition of Howard would improve all three ratings.
Howard is a three-time Defensive Player of the Year for good reason: He covers the paint like a blanket. He blocks shots and alters shots and causes teams to shoot farther from the net than they ordinarily would, which lowers their shooting percentage.
When he leaves the paint, he's effective too, slowing down running attacks and disrupting pick-and-rolls.
Further, his defense can actually win the Rockets more games. Per Basketball-Reference.com, in the last six years, Howard has led the league in defensive win shares four times, came in third in 2011-12 and came in sixth this season.
Heck, at the MIT Sloan Sports Analytics Conference—where Rockets general manager Daryl Morey is the equivalent of Justin Timberlake—an entire paper about interior defense analytics was entitled "The Dwight Effect." Here are highlights:
…it could be argued that Howard’s mere presence “blocks” shots before they happen. The presence of a truly dominant interior force can augment the spatial behavior of the offense in the same way that a dominant cornerback changes the behavior of a quarterback. While it is easy to tally up things like blocks, rebounds, and steals, it’s much harder to measure the kind of disruption or the strategic augmentations that dominant interior defenders like Dwight Howard create. We define “The Dwight Effect” as the ability of an interior defender to reduce the efficiency of an opponent’s shooting behavior.
When statistical research papers are named after you, it's clear that you're the gold standard when it comes to defense.
As recently as two years ago—before he essentially flashed his old team the middle digit—Orlando Magic TV commentator Matt Guokas called Howard a better defender than Bill Russell, according to Mike Bianchi of the Orlando Sentinel. And the NBA invented goaltending in an attempt to neutralize Russell—that's how dominant he was.
Yes, Howard came in 14th in DPOY voting this year. But if he is healthy, there is every reason to believe he would return to his previous lofty standards. Simply put, he is a game-changer on defense.
Which is perfect for the Rockets, who definitely need to change their game on that side of the ball.