Jesus De La Villa's 100 Endgames book: Ambiguity Here we have two scenarios where the stronger side has one passed pawn in a KPP vs. KP ending. The other pawns block each other.

In Ending 83, the author states that rook's pawns, if they're not blocked, should be advanced as far as possible. But in Ending 85, he concludes that the stronger side always wins with a passed bishop's pawn (on the same wing) if the rook pawn has remained on the second rank (i.e. not advanced). 

Should the rook's pawn be advanced or not?
Those endgames are fundamentally different - one has rook pawns and a distant passed pawn (83); the second has rook pawns and a passed bishop pawn on the same wing (85).

The reason in the second case (85) is you may need a tempo move with the rook pawn on its original square. It's explained very clearly in the book.