Begiristain's appointment has been interpreted in some quarters as a blow to Mancini, as the Spaniard will have control over player recruitment.
But the manager said: "I am very happy. He has a lot of experience with a top club like Barca.
"If we did well in the last two years, I think we can do better in the future.
"It is very important for this reason. He worked with Barca and won everything with this club.
"He built a fantastic team with Barca and for this reason I think, for us, he will be very important."