Maholm is a having a solid year with a 3.74 ERA (4.30 carer) and a 1.238 WHIP. He should fit into the Braves rotation as the fourth or fifth starter, giving the rotation two left-handed starters. In his last seven starts, Maholm is 5-0 with a 1.00 ERA.
Johnson gives the Braves a veteran outfielder and right-handed bench bat. Atlanta has been searching for an additional right-handed bat all year, but with the injury to Matt Diaz, it became necessary to acquire another right-handed option. Johnson is hitting .307/.361/.452 this season, which are a tick above his career numbers.
Maholm has a team option on his contract for next season at $$6.5 million, so if the Braves choose to keep him around beyond this season they can, at a relatively affordable price -- especially if he continues to pitch like he has been. Johnson is a free agent at the end of the season.
Vizcaino is the prize in this trade for Chicago. He is currently out for the season after Tommy John surgery at the end of spring training, but he should return at some point next year. When healthy he's a dominant reliever, and could also be used as a starter, with the potential to be a top-of-the rotation guy.
Reliever Jaye Chapman has been in the Braves system for seven years, and is way down on the bullpen depth chart. He's got a classic middle reliever profile, but he's a bit old at 25 to be considered a prospect.
Vizcaino has some great upside, but he hasn't been healthy for a full season since he arrived in the Atlanta system in the Javier Vazquez trade with the Yankees. He was considered untouchable during trading season last year, but the Braves seem to have eased the "untouchable" label on their prospects. Best of all the Braves keep their pitching prospect depth, retaining Teheran and Delgado, both of whom are healthy and could help this year if needed.
I would rate this a really good trade for the Braves, maybe even great. Atlanta gets a perfect fit in outfielder slash right-handed pinch-hitter Reed Johnson, and a solid (and lately spectacular) pitcher in Paul Maholm. All they give up are two relievers, one of whom is out for the year and the other of which didn't seem to fit into the Braves plans. That's trading from an area of great depth for two critical needs in the middle of a pennant race. Really good trade.