KKtP

If White accepts the sacrifice, he loses his KKtP, and Black retains three passed pawns for the piece, at least an equivalent for the end-game.

R-Kt5 Not RxP, on account of R-B7, and the KKtP cannot be saved.

He can then either aim at the White centre at once with P-KB3, or else play P-KB4 and prepare the advance of the KKtP by Kt-B3-Q1-B2.

Now Black forces the advance of White's KKtP, and the Bishops become immediately effective.

Both the KKtP and KBP would be weak, with the King on the other wing, and be under constant threat of being captured.