Clarification in the book Logical Chess, Move by Move, by Chernev I am working through the book mentioned and in game 8 (Przepiorka vs Prokes) at move 4 ...P-B4, which is black moves pawn to C5.  The book states the following:  "This move is almost indispensable in Queen Pawn openings.  It is important not to play ...Kt-C6 first, as the bishop pawn must not be obstructed."  Could someone shed some light on the importance of ensuring the queen's bishop pawn is unobstructed?
Often black plays b6/Bb7/c5 to support an attack against the White d-pawn, and at times even Na6 to support c5. Obstructing the c-pawn slows down or prevents these kinds of maneuvers. Nc6 is an awkward placement of the knight on the queenside with d5/e6 being played by black, as it has no real good second move from c6 to get out of the c-pawns way, thus losing time, if black wants to follow up with ...c6 or ...c5. The move ...c5 is a "breaking" move that black wants in many openings, including the Caro-Kann, the French, etc., and not just d-pawn openings. A knight on c6 is generally speaking a 'good' knight when ...e5 and/or ...c5 has been played, i.e., king's pawn openings, The Sicilian Defense, etc.