Black's last move was ...Bf6. You have two options: a) Take a queen on d5 and take it to a Bishop of opposite colors with a Bishop of White Squares; b) Take a queen on f6 and take it to a Bishop of opposite colors with a Bishop of Dark Squares; Which would you choose?
Its the same thing but taking on f6 is better because black has already weakened their dark-squares and it also saves us a tempo on the rook (if Qxd5, Bxb2 with a tempo on the rook).
Black's last move was ...Bf6. You have two options:
a) Take a queen on d5 and take it to a Bishop of opposite colors with a Bishop of White Squares;
b) Take a queen on f6 and take it to a Bishop of opposite colors with a Bishop of Dark Squares;
Which would you choose?