Jason Vargas gives up homers. Like, lots of homers. Since joining the Mariners in the majors in 2009, Vargas has allowed 91 homers in 702 innings, a rate that wouldn't be much worse than league-average except for one small detail: his home park is one of the most-significant homer-depressing stadiums in the game, especially so for the right-handed batters this lefty has struggled mightily against.
Of the 108 homers Vargas has allowed in 829 career innings, 34 came at Safeco. In Seattle, his home runs per nine sits at 0.8, a more than respectable figure that a pitcher can certainly succeed with. Outside of its walls, however, including his years prior to his switch to Seattle, Vargas has allowed 1.5 homers per nine. There's a trickle-down effect, too, as Vargas can pitch differently at home with success than he can on the road, where errors are more costly for him.
At Safeco, his strikeout-to-walk ratio is 2.6, whereas everywhere else it's 1.8. Vargas can attack hitters at Safeco more, knowing he's safer there from retribution for it than he is in most other parks, especially most other American League ones. If he should leave a ball up in the zone, or over the fat part of the plate, the dimensions and environment of Safeco can save him, at least more so than elsewhere. He has to nibble a bit more outside of that park, resulting in the lower K/BB, but even with that, there are far more balls going yard, as well as a significantly lesser punch out rate (6.1 per nine at Safeco, compared to 5.4 everywhere else.
In a Vargas-shaped nutshell, all this means is that leaving the comfort of Safeco is a problem for the pitcher. It might be a little less of a problem in his new home, however, than it could be elsewhere. Angels Stadium of Anaheim isn't quite the problem for right-handed power that Safeco is, but it's still one of the tougher parks around to go deep in. Whereas Safeco has reduced homers for right-handed batters by 30 percent in the last three years, per Stat Corner, Angels Stadium has down so by 20 percent. This likely means Vargas is going to see an increase in homers compared to his own three-year rates -- one he certainly doesn't need -- but it could be a lot worse if he had been traded to, say, the Rangers.
As it is, Vargas is kind of a fringe fantasy pitcher in mixed leagues. He has innings, and his ERA tend to be low, but the lack of strikeouts can be a bit of a drag. Taking him out of Safeco won't help matters, but at least he won't have to face the Angels' lineup anymore. Small miracles and all that. In AL-only leagues, Vargas has far more value simply due to a lesser pool of pitchers to pull from. And, while this would have also counted were he still in Seattle, he's going to get to face the Astros quite a few times per year now, given they are now in the AL East, so there's that to consider as well.
All told, though, he's a guy you're probably only going to want in this AL-only formats, unless you can afford to carry a home-only pitcher on your roster. In that case, he won't be as good at home as he's been in the past, but it'll sure beat what he delivers to you on a road trip.