Ulhumbrus: The move 14...Bxf3 concedes the bishop pair to White, following the recapture 15 Bxf3.
This suggests the question: What is White going to do with this bishop pair?
The queation will begin to be answered twelve moves later at move 27, but first the move 16 Nb1 frees the c pawn for the move 18 c3, and 19 Nb1-d2 redevelops the N to d2. Then White's Queen takes six moves to make her way to d3 via b1, c2, b3, c4 and e2.
Following the move 26 a3, the move 27 b4 begins to provide an answer to the question: the player who has the bishop pair is at greater liberty to advance his pawns. The pawns become a weapon instead of a target.
The advance gains White greater space on the Queen side and then the manoeuvre Nd2-c4-a5 begins a Queen side attack. White's Queen side attack ends up winning a pawn on the Queen side by means of the capture 34 Qxb5.
In return Black wins a pawn on the King side, but as before, Black's pawns are less free to advance than White's.
Petrosian relinquishes his bishop pair by 37 Bxe6 in return for crippling Black's King side pawns after the recapture 37...fxe6 when Black has doubled isolated pawns on e6 and e5.
After a few further moves Sax resigns, perhaps seeing no satisfactoru answer to the advance of White's Queen side a pawn.
We can now, at the rish of repetition, answer the question of what White gains from the bishop pair. The first thing which White gains consists of increased liberty to move for his Queen side pawns. The advance of White's Queen side pawns leads to a Queen side attack which wins a pawn on the Queen side. Black is able to win in return for a pawn on the King side.
Then however White is able to use one of a second power of the bishop pair to cripple Black's King side pawn majority, by relinquishing a bishop for Black's N. Either Bishop is able to attack Black's Knight from a distance, and White attacks Black's Knight with his King's Bishop and exchanges it for the Knight. After that Black has no compensation for White's Queen side passed pawn and no satisfactory answer to the threat of the advance of White's passed a pawn towards coronation.