Iglesias is a better reliever than Will Smith, so this is an upgrade for this year. He could pick up a handful of saves this year. If Jansen goes down or is unavailable for a game, he will likely close. Iglesias will likely play a similar role as Will Smith did. Jansen has been the closer all season, except for when injured/out, and has done nothing to lose it. But the closer game isn't about skills always it is about the opportunity as well.
When looking at the peripheral stats, Jansen isn't *that* much better than Iglesias it's pretty even. Jansen is fourth in saves and has blown four saves this year along with a 3.43 ERA, 2.98 xFIP, and a 34.6% strikeout rate, which is just a smidge above Iglesias' 32.9% strikeout rate. In Atlanta, they have their closer in Kenley Jansen. Iglesias was still a top-20 closer and someone one would start every week in hopes that the Angels would improve and he would get more saves. Yes, his ERA could be lower and yes, his strikeout rate has gone down, but he was drafted mainly for saves as most closers when healthy pitch 60-70 innings per year. The Angels are just so bad at 44-59 that there just aren't many save opportunities overall. He has just three blown saves on the season. He has a 4.04 ERA and 16 saves, which puts him at 16th in saves this season.
He was drafted in the NFBC near the top-50 and was taken as a top-three or four closer. Prior to this trade, Raisel Iglesias was the established closer for the Angels but putting up a somewhat disappointing season.