Why and when should one make a zwischenzug (in-between move)? I know enough German to know that the term &quot;zwischenzug &quot; means &quot;in-between move.&quot; Another translation I've seen is an &quot;interpolative&quot; move. Why make such a move?
An example is when a rook wants to go to the seventh rank. First, it goes to the eighth rank, let's say with check, and when the opponent replies, the rook goes back to the seventh. What might be the advantage of using such a &quot;roundabout&quot; route to get to the seventh rank?
In GO (where I'm higher rated than in chess), it might be called a forcing move. You make a &quot;throwaway&quot; move that forces a particular response, and then you make your main move, and the two together are stronger than making the main move alone. How might this work in chess?
That's really an enormously broad question. The answer is "because it's a good move, sometimes." :-)

Let's say one player expects the game to go "I take here, then he takes there, I take there, he takes there, I take back the rook... and I end up a pawn up."

What happens is "I take here, he takes there, I take there, he moves the rook with check, I have to move my king, he takes there, I can't take back the rook... and I end up a rook down."

That's the sort of situation where a zwischenzug helps. When what at first looks like a forced sequence of moves can actually have an extra move added to the middle of it that makes the end result better for the side doing it.

Turning this into some actual position with a diagram and such is left as an exercise for the reader.