"Some pitches I do want to swing and miss on," said Cubs outfielder Chris Coghlan when he appeared on a recent edition of the Statcast™ podcast. "When I'm fooled, I want to swing and miss, I don't want to tap out and be [happy] that I put the ball in play and didn't strike out."
In a sport that's recently become enamored with making more contact to stem the strikeout tide, the truth remains that not all contact is created equal. There's good contact, and then there's the weak contact that you'd be better off not making at all. It's the baseball equivalent of "live to fight another day," and as Coghlan noted, there are worse things than swinging and missing, particularly with fewer than two strikes.
We can -- and will -- pull some traditional stats to help back that up, but given that we now have Statcast™ at our disposal, let's start with the simplest definition of "good contact," which is using exit velocity to see how hard a ball was hit. With the safe assumption that pitchers are forever trying to induce hitters to make weak contact on bad pitches outside of the zone, we can start by seeing how much harder batters can hit the ball on pitches inside the zone than out:
Exit velocity, MLB, 2015
In strike zone: 91.0 mph
Out of zone: 83.2 mph
That's a pretty massive margin. Put another way, contact made in the zone makes every batter hit the ball like they're Justin Upton, while outside the zone turns everyone into Kris Negron. Since we know that exit velocity correlates pretty well to offensive production, it's an important distinction. Swinging at good pitches, while overly simplistic, is basically the best thing a hitter can do.
The "in the zone" exit velocity leaders shouldn't surprise you, since they're led by Giancarlo Stanton, Ryan Braun, Miguel Cabrera and Mike Trout. (Although since Stanton's in-zone average of 100.4 mph basically makes him the hitting equivalent of Aroldis Chapman each time he touches a ball in the strike zone, you start to wonder why he ever actually sees a hittable pitch.)
It's not that good contact can't ever be made outside the zone, of course. Cabrera is second on that list too, behind only Justin Bour (89.9 mph), of all people. But literally every hitter in our sample of 276 hit the ball harder on pitches in the zone than outside it. It's basically an irrefutable fact, and the story doesn't change with more traditional stats:
Batting average, MLB, 2015
In zone: .300
Out of zone: .188
Slugging percentage, MLB, 2015
In zone: .502
Out of zone: .263
As far as batting average goes, that's the equivalent of Trout inside the zone and Chris Iannetta outside it. Slugging is even starker; a .502 mark is Jose Abreu or Manny Machado, but .263 is, well, no big leaguer who had at least 250 plate appearances slugged that poorly, so, you can't do that and be a big league non-pitcher, apparently.
Now, none of this should be shocking. Of course you'd expect balls in the zone to be hit harder, and hitters know that. Of course, pitchers know that too, and each year they're throwing fewer pitches in the zone...

...despite throwing more and more first-pitch strikes, up each year from 2009's 58.2 percent to 2015's 60.9 percent. What that means is that pitchers know that hitters are too often watching hittable first pitches fly by in hopes of working the pitch count, but that's an offensive strategy that's long past its expiration date. For example, hitters down two strikes would see only 33.2 percent of pitches in the zone, as compared to 43 percent leading off an at-bat.
It's easy to say that this is something we've always known, that it's better to swing at strikes than balls, and that's true. But it's also interesting that we can now put the numbers to it, to look at the exit velocity and hitting production and see just how jarring the differences are. If you're often swinging outside the zone, like Pablo Sandoval (46.8 outside zone swing percentage) and Avisail Garcia (44.8), you may be in trouble. If you're not, like Joey Votto (19.2), Jose Bautista (21.1) and Paul Goldschmidt (22.0), good things can happen.
As for Coghlan? Well, he's not wrong. On balls inside the strike zone, Coghlan's exit velocity was at 90.4 mph, which went with a .318 average. Outside the zone, it was just 83.4 mph, and a mere .106 average. The same story applies to every hitter in baseball. It's great to make contact. Sometimes, it's better not to.