Another questionable decision. This pawn can well become a weakness very soon. Why should one voluntarily advance pawns on the side where one is weaker?
1. d2d4  1... g8f6  2. c2c4  2... g7g6  3. g1f3  3... f8g7  4. e2e3  4... e8g8  5. f1e2  5... d7d6  6. b1c3  6... b8d7  7. e1g1  7... e7e5  8. b2b3 A somewhat slow move. Since the center will  be closed soon and both sides will have clear plans of playing on separate flanks, it made sense for White to push this pawn on b4 at once. 8... f8e8 