The concept of the blockade was developed by Aron Nimzowitsch in his influential book "My System." Nimzowitsch argued that the best way to deal with a passed pawn or a strong central pawn is not to attack it immediately but to place a piece in front of it, permanently preventing its advance.
Knights are ideal blockaders because they do not lose any mobility when placed in front of a pawn — a knight on d5 blocking a d-pawn controls the same squares regardless of the pawn behind it. Bishops, by contrast, are poor blockaders because a pawn on their diagonal limits their scope. Rooks should rarely blockade because their strength lies in open files.
After establishing a blockade, the next step is often to pile up pressure on the immobilized pawn with other pieces. Since the pawn cannot advance, it becomes a static target. The blockading piece serves double duty: it restrains the pawn while occupying what is typically a strong outpost.