Yes, the brilliant tactical point of Nimzowitsch's 12 ... a4!! is 13 axb4? ♘xb4 14 ♕b1? ♘b3#, a beautiful picturesque pure checkmate from the Black knights:

click for larger view

Is 12...a4 really such a wonderful move?

What does it do to aid Nimzowitsch's position?

The bishop on b4 is still immune no matter which move Nimzowitsch makes on turn 12.

If the purpose of 12...a4 is to tempt Bogoljubov into blundering, it didn't work.

It would likely work on me, but not against world class opposition.

So on move 12, Nimzowitsch can afford simply to develop another piece, if he so wishes.

Albert Becker annotations to the game (Wiener Schachzeitung, March 1930, pp. 76-77) may shed some light on the issue:

He critisizes 9.e3<?>, suggesting the manoeuvre <9.a3 Bxc3 10.Bxc3 0-0 11.b4 Ne4 12.Bb2> with excellent play. White hoped to execute the plan later, but he errs.

On 10.Be2, he notes that now <10.a3 Bxc3 11.Bxc3> is meat with <11...a5!> (and plater possibly <...a4>) and this prevents <12.b4? axb4 13.axb4 Nxb4! etc.>.

11...a5 receives an <!>, and is called the initation of an ingenious attack.

12.a3<?> is called a decisive mistake, since the hole on b3 is perversive of White's play. He suggests <12.Nd4!> instead.

12...a4 receives <!!> and he gives two beautiful mating lines, if White takes on b4 on moves 13 or 14.

I do not know if Becker's analysis stands up to strong modern engines, but it's certainly interesting to see which plans a strong contemporaneous master like Becker identifies in that position.

A plan involving b4 was considered fine for White. On move 9, he could have tried it. It would not have been that easy on later stages. 11.0-0-0 was not annotated, but 11.0-0 may have been better.

Thanks <Karpova>!

It doesn't. In particular SF likes <12.a3> which Becker called a decisive mistake and SF doesn't think much of <12...a4>.

But that's not the most important thing. Nimzowitsch was playing a human and your own final paragraph explains nicely why a human wouldn't want to face 12...a4 and thus why <ray keene> would describe it as "a wonderful move".

<11.0-0-0 was not annotated, but 11.0-0 may have been better.>

With almost all of the kibitzing focusing on the opening it's worth keeping in mind that Bogoljubov came out of it alive and still in the game (if maybe a little cornered).

In fact Nimzowitsch had let him off the hook to a large degree with <18...Qc7?> when <18...Bxc4! 19.Rxd8 Raxd8 20.e7 Nab3+ 21.Kb1 Bd3> would have seen him a piece to the good.

Believe <ray keene> mentions this gaffe in his annotations in <Nimzowitsch: A Reappraisal>.