While working through "Perfect Your Chess", I decided to take a break and play a couple of online games on FICS.
I arrived at the following position. It's Black to play.
Black is under a bit of pressure. I find that going through the tactics book is starting to have some effect on my game.
I break down my line of thought as follows:
White has an extremely dangerous b-passed pawn and the only open file is the a-file and guarded by White's rook. If Black does not do something now, the White Knight on f1 becomes active and together with the b-passed pawn, Black will forced to be on the back foot for a long time.
Now have a look at White's pawn chain, the pawn chain while residing on dark squares, the Bishop lacks scope and dreadfully out of place and attacking the base of the pawn chain with the bishop takes too many moves.
However, there is a way to regain the initiative. Looking at this position, I played
1..... Bxb5! Sacrificing the bishop.
Why is it necessary to sacrifice the bishop here?
a. The bishop is not doing anything useful
b. White's pawn chain is very hard to break down.
c. Awkward placement of White's knight on f1 and possible back rank mate tricks.
d. 2 pawns for the sacrifice
e. The black c-pawn now become a dangerous passed pawn
f. The Black king is relatively safe
g. The Black Rook now has activity with an open b-file to work on
So after 2. cxb5 Rxb5 ... play becomes considerably sharper and the initiative has been passed to the Black side and it is White who must now tread carefully.
I won't bore you with the rest of the game but suffice it to say that White was forced to give back the piece and Black won eventually after a somewhat prolonged struggle. I was quite satisfied with this game.
Of course not every sacrifice works. When going for a sacrifice, especially an exchange sacrifice, both the short term and the long term strategy and aspects of the position must be taken into account and it is here where I spent a lot of time calculating lines and other variations. I have to say that it took me a long time before I decided to sac the bishop and I wasn't 100% certain it would work but it "looked" workable.
I am still trying to understand how exchange sacrifices work and how to fathom when such a strategy works and when it does not, especially in dynamic positions. It's definitely not easy.