In the Sicilian Najdorf poisoned pawn variation what is the difference between including the moves 7...h6 8 Bh4 (as many top players do) and not including them?

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1.e4 c5 2.Nf3 d6 3.d4 cxd4 4.Nxd4 Nf6 5.Nc3 a6 6. Bg5 e6 7. f4 Qb6 (7...h6 8. Bh4 Qb6 9. Qd2 Qxb2) 8. Qd2 Qxb2