What do the c5 and e5 breaks do in the Caro-Kann / Scandi pawn structures?

Question

Here's what I understand about the point of c5 in the French / Advance Caro-Kann pawn structures: if White takes you are very happy, because his e-pawn becomes weak and you get to develop your bishop to a nice active square in one move. Even if he doesn't take, it opens up some breathing room for your pieces, eg. you can play moves like Nc6 and Qb6 to further pressure the d-pawn, eventually play cxd4 to fix the weak pawn on d4 and open up the c-file, etc.

However, I don't understand why it's as desirable in Scandi / Caro-Kann pawn structures where Black has played dxe4. In these structures:

• White has not committed a pawn to e5, so you are not making it weak.
• In most cases you've already developed your bishop to e7 or d6, so it's not like you will be saving a tempo if he captures.
• Also in most cases, you have already played Nd7 so you're not gaining the c6 square for your knight.
• You've already placed c6, so your queen can already access the a5-d8 diagonal.
• If you capture on d4, White can just recapture with a piece without having to worry about the pawn on e5 becoming weak.

So, in concrete terms, what does Black gain from playing c5 in these structures? (And ditto for e5.)

Answer 1

You misunderstand the principle reason for playing c5 in the French Defense. It doesn't matter whether or not white has already played e5. It doesn't matter whether or not you have or will soon develop the f8 bishop. You play c5 to attack white's center and in particular the pawn on d4.

It then follows that if white responds to c5 with c3 defending the d4 pawn then you are not in a rush to play cxd4 because you are really just swapping c pawns and yours is slightly better.

If white plays the advance variation then a key black move is f6 to attack the e5 pawn and undermine white's large center.

Exactly the same principles apply to the c5 and e5 breaks in the Caro Kann, Scandinavian and for that matter the Benoni and King's Indian Defence. In all of these openings it is vital for black to attack and undermine white's center else black is likely to get rolled over.

Answer 2

C5 and e5 are the only pawn breaks in the position so it feels like there's not much else for black to do. Usually e5 is harder for black to achieve because white's pieces cover e5 from their natural squares (e.g. Re1, Nf3).

In the Caro/Scandi structure white tends to be slightly better and black's plans mostly aim to equalize the game. As long as white has his pawn on d4, he's the only one having a pawn in the centre. That gives white more space and control of the board. So it makes sense for black to try to exchange his c-pawn for white's central pawn. The resulting 3-3 vs 2-4 pawn formation is fairly drawish but both players have their chances. Usually an extra pawn on the queen side is a very slight endgame advantage for white but in some cases black can try to create a minority attack.