Luis Enrique prefers to combine the presence of one of them with a more attacking midfielder
Xavi and Iniesta were part of the best midfield in Barça's history, along Sergio Busquets. Since Guardiola, Tito and Tata, two key players to Barça's game style. But when Luis Enrique arrived the story has changed.
Since the defeat against Real Sociedad at the beginning of the year, both Barça players keep on being irreplaceable for the coach, but not together. He only made them play along each other in 11 minutes of the 14 matches (1260 minutes) that have been played since then (8 La Liga, 5 Copa del Rey and 1 Champions League). Specifically, Xavi and Iniesta coincided on the pitch in the first-leg match of Copa del Rey against Atletico Madrid.
With Luis Enrique, Barça have adopted a more attacking game than last year, thus, the coach choses one of the two players, rules of possession game, with more attacking profile of the attacking player, like Rafinha or Rakitic. Actually, the Croatian is the player who played more minutes on the midfield this 2015 (780'), if we take away Mascherano (1049) or Busquets (892') with a behind position.
There are only two matches without Xavi nor Iniesta: both from the Copa del Rey qualifying round against Elche.