b5 doesn’t necessarily have to be combined with Bb7 of course. In many lines Bd7 or Be6 and Rc8 is played as a follow-up.
a6, b5 and Rc8 are part of the mighty minority attack - the goal which is paramount in the glorious Sicilian. I quote myself:
„The Sicilian cheap trick - a superior structure with an extra center pawn, semi-open c-file and minority attack. The only problem is to survive white‘s first strike.
May I quote "Simple Chess", the famous book by M. Stean? Believe it or not, it's 40 years old! Could be written yesterday.
"Minority attacks derive from the Pawn structure, Pawn structures derive from the opening. Go back to the eras of Capablanca and Alekhine and you will see Queen's Gambits, hoards of them, with hoards of minority attacks descending from them. Nowadays [1978; still relevant] the Sicilian Defense is all the rage. Sicilians here, Sicilians there, Sicilians absolutely everywhere. Why this saturation with Sicilians? Does the Mafia's influence really extend this far? The answer lies in the minority attack. The whole idea of the Sicilian is for Black to trade his c Pawn for the d Pawn. White almost invariably obliges: 1.e4 c5 2.Nf3 Nc6 (or d6 or e6 or g6) 3.d4 cxd4, when Black immediately arrives at a minority attack Pawn structure. Half-open c file, extra central pawn, 2-3 minority on the Queenside; these are all the necessary ingredients. Sounds infallible, so where's the snag? Why doesn't Black win every game? The problem is of course that White has a lead in development in the early stages, which may prove difficult to survive. Black's prospects lie later in the game when the winds of White's initiative have blown themselves out."
The structural weaknesses White accepts because he is trying to avoid Black's plan to launch a minority attack to get a winning endgame and must attack. They are not the cause of Black having winning endgames (otherwise White wouldn't weaken his position in such a way); merely they are a symptom of him having to attack the Black King. The root cause of this is the minority attack, and this is why most Sicilian endgames are winning for him. The minority attack is also a theme in any Rook endgames, so it's not just a late middlegame idea."“
a6, b5 and Rc8 are part of the mighty minority attack - the goal which is paramount in the glorious Sicilian. I quote myself:
„The Sicilian cheap trick - a superior structure with an extra center pawn, semi-open c-file and minority attack. The only problem is to survive white‘s first strike.
May I quote "Simple Chess", the famous book by M. Stean? Believe it or not, it's 40 years old! Could be written yesterday.
"Minority attacks derive from the Pawn structure, Pawn structures derive from the opening. Go back to the eras of Capablanca and Alekhine and you will see Queen's Gambits, hoards of them, with hoards of minority attacks descending from them. Nowadays [1978; still relevant] the Sicilian Defense is all the rage. Sicilians here, Sicilians there, Sicilians absolutely everywhere. Why this saturation with Sicilians? Does the Mafia's influence really extend this far? The answer lies in the minority attack. The whole idea of the Sicilian is for Black to trade his c Pawn for the d Pawn. White almost invariably obliges: 1.e4 c5 2.Nf3 Nc6 (or d6 or e6 or g6) 3.d4 cxd4, when Black immediately arrives at a minority attack Pawn structure. Half-open c file, extra central pawn, 2-3 minority on the Queenside; these are all the necessary ingredients. Sounds infallible, so where's the snag? Why doesn't Black win every game? The problem is of course that White has a lead in development in the early stages, which may prove difficult to survive. Black's prospects lie later in the game when the winds of White's initiative have blown themselves out."
The structural weaknesses White accepts because he is trying to avoid Black's plan to launch a minority attack to get a winning endgame and must attack. They are not the cause of Black having winning endgames (otherwise White wouldn't weaken his position in such a way); merely they are a symptom of him having to attack the Black King. The root cause of this is the minority attack, and this is why most Sicilian endgames are winning for him. The minority attack is also a theme in any Rook endgames, so it's not just a late middlegame idea."“