Parra is a 30-year-old lefty who seems to have been brought on to be the club's new left-handed specialist now that Aroldis Chapman has moved to the starting rotation and Bill Bray has signed a minor league deal with the Washington Nationals.
The problem with him being a left-handed specialist is that he's, well, not a specialist.
Check out his splits against right-handed and left-handed batters (per fangraphs.com)
Parra isn't a specialist, quite simply because he's equally bad against batters on both sides of the plate.
So what exactly is Parra's role on the team going to be?
Parra can eat some innings and can definitely strike batters out.
Over the course of his career, Parra owns a K/9 value of 8.40 K/9. But unfortunately, he's going to walk batters at an unacceptably high rate for a reliever (4.60 BB/9).
Outside of the fact that he hasn't pitched very well over the course of his career, he wasn't even the best left-handed reliever available.
Hideki Okajima, Rich Hill, Rafael Perez and J.C. Romero are all still available (per MLBtraderumors.com free agents list).
Romero, Hill and Okajima all have splits that indicate their ability to get left-handed hitters out at a more efficient rate than they do left-handers (click the links on their names for career splits).
Though he is slightly better against right-handed hitters, Perez is still more efficient than Parra against batters from both sides of the plate (see Perez splits here).
The fact that the Reds signed Parra when these four relievers are still available seems odd, but maybe they see something in him, the same way they saw something in Jose Arredondo when they signed him following an injury.
But for now, Parra shows no signs of being a good signing for the Reds.