The power of the passed pawn

Continuing my recent look at endings, I present the following nice position from 1911. In this case Tarrasch got one over his rival Nimzowitsch by knowing exactly when to swap into a apawnending, and then knowing what to do after that.
It is also an example of what I regard as 'playing by knowing'. I'm assuming that Tarrasch worked out the winning line over the board, but for the rest of use, it is now enough that we can remember the example to use it in our own games. Of course this assumes that there is enough spare room in our heads to store such items, but 'knowing' this idea is probably preferable to having to work it out.
In the game Tarrasch (as black) finished off Nimzowitsch with 1. ... Rb5 2.Kg4 (to get back to the a file asap) Rxg5 3.Kxg5 a5 4.Ke4 f5+!! (The winning idea. If 5.Kxf5 then the a pawn queens) 5.Kd4 f4! Now White cannot play g3. While the White king is dealing with the a pawn, Black can play Kg6-h5xh4 and wins. The f pawn had to reach f4 to stop White protecting the h pawn with g3.