At the beginning of the year, the Houston Astros had a problem in the bullpen by the name of Ken Giles. When Giles proved ineffective and had his second meltdown, the Astros made the reliable Hector Rondon the new closer. At the trade deadline, the Astros shipped away Giles in return for Roberto Osuna. Along with the baggage that came with Osuna, they got a better closer for the playoffs.
While Rondon has gotten some saves here and there, Osuna is the primary choice to close a ballgame. There may be times where the matchups favor using Rondon, but he has been shaky recently.