Why do we need to exchange black bishop in A43 Benoni Defense?

Question

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The only reason for developing the black bishop was to snipe the border during middle game and endgame, but in the opening itself, stockfish 14 tells me to exchange the bishop against queens gambit setup.

Why is that?

Answer 1

Same as in Nimzo-Indian. Bxc3 has two different effects that must be weighted against each other:

• The white pawn structure is dead meat now, especially the Pc4 will have a nightmare. The attack can be done exactly like in the Nimzo, although some Na5 is far beyond the horizon. Even better, the Nimzo typical Pd4 is already on d5 (so to say), so White has no mobile pawn center.
• White, as in the Nimzo, will pay back with a direct attack on the king. Black misses the fianchetto bishop dearly and White has the bishop pair. But note that even if Black castles short, it is not so easy to find use for it (no place for the Bc1 on the long diagonal).

The latter, for a long time, lead to anyone brushing off Bxc3 as a death wish. It isn't. Black usually even (after the exchange) continues to laugh about opening principles and plays f5, with a fat 32:29:40 score out of 500 games (even though Stockfish still gives White a minimal advantage). But never trust any statistic you didn't fake yourself, just one move later White packs out e4 followed by the gambit f3 (the first thing I would think of myself) and a fantastic score...unless again Black says "Eat my shorts", plays e5 to ignore the gambit and again has the upper hand...

I tell this all just as a warning: isolated data is as bad as isolated pawns. Tournament praxis is a much better indicator whether a variation is sound. Here are some further positional considerations for this variation.

Answer 2

You don't "need" to exchange your dark-squared bishop, but it is definitely a great option to consider. A "standard" Benoni play would consist of some sort of ...d6 and ...e6 play on the center, but White is probably going to be comfortable there and has many options available.

Another option available to Black is to counter White's space advantage by playing an immediate ...e5, but this would make the g7 bishop a horrible piece, that's why trading it on c3 may not be the worst of ideas. In fact, 4...Bxc3 5.bxc3 e5 is a quite successful continuation for Black.

Whether Black opts for an ...e5 push or not, Hauke Redmann's points still apply: another benefit of trading the bishop for the knight is the damage you cause on White's pawn structure. Black can create pressure on the queenside by attacking the weak enemy "c" pawns, but it's not always easy to capitalize on that (there's no clear plan to coordinate Black's minor pieces for an attack on those pawns).

As a final note, when discussing openings, please take into account that "it takes two to tango". White can't play a Queen's Gambit unless Blacks allows him to. The position we're talking about is a Benoni. Not a Benoni by Black against White's Queen's Gambit, just a Benoni. And it wouldn't have been so had White not played their pawn to d5