Playing at (1,2) creates two potential winning paths: a horizontal opportunity along the middle row and a diagonal opportunity. This forces the opponent to block one of these threats, while leaving the other open for a potential win on my next turn. If they block the horizontal threat at (1,0), I can win diagonally by playing at (2,1). If they block the diagonal threat at (2,1), I can win horizontally by playing at (1,0).