Real Madrid has some players that are good on their bench but they are not used most often by Anceloti to demonstrate their effort on the big games. He is using a set and doesn't make changes often, though it's good because what he aim is always achieved and what is the used of changing players when clearly he can win the game with the main squad that he has, perhaps the bench ones will used this opportunity to show him their best.
I quite respect the way Ancelotti manages his team, having the first 11 squads always in the forefront and preparing other good players as alternatives too. It shows how he understands the stamina of his squad and where and when to shuffle them. He's a coach that works with much calculations and always ready to take decisions while withstanding the demands that comes with working with such a top class team which sometimes suffer player injuries and instability in the understanding of the old and new players.
I think one of the advantages of having Carlo Ancelotti as the manager of Real Madrid is the wealth of his experience. For a manager who's the league title in each of the top five leagues in Europe, understanding how football works isn't an issue for him again. He's mastered the art of squad rotation and that's why he rarely makes mistakes with his choices. Some of the players at Real Madrid who mostly start important games from bench will make the first XI of some of the top teams in Europe so you should know that for them to be happy to play under Carlo Ancelotti even when a starting shirt isn't guaranteed is a testament of the Italian manager's expertise