user598: In game 11 of the 1972 World Championship, Spassky as white moves his Knight back to its 14. Nb1 starting position. Apparently, this moved was received as 14. Nb1!!. But to me, it seems as a simple attack on the invading black queen to flush her out of the zone.
What about this move makes it so interesting?
Shown below is after move 13. Kh1 Bd7
[FEN "r3kb1r/1p1b1p2/p1nppp1p/8/4PP2/qNN5/P1PQB1PP/R4R1K w - - 0 1"]


user2001: The idea Nc3-b1 has gradually become well known. In general, the idea is to get the knight to a better square, e.g. the c4 square. Another consequence is that the a1-h8 diagonal opens and can be controlled by the white queen at some point. The third is that the c2-pawn can move forward. In this position, white wants to attack, but has to mobilize the forces first. Nc3-b1 can at first seem to help the black queen to return to c7, where it will be safer. At the same time, the knight can continue with Nb1-a3-c4 and attack the d6 and b6 squares. Another option is to place the c2-pawn on c4 and do Qd2-b2 to control the a1-h8 diagonal. What makes Nc3-b1 special is that it allows white to regroup the forces and then follow up with an attack.

user17: White has completed his development, and Black has not, giving White an advantage. The reason this is true is because of Black's queen moves.
Therefore, the way to prevent Black from completing his development is to harass the queen. When the smoke clears, White will have a clear advantage in development, going into the endgame, making him a heavy favorite. 

user307: Taking a look at the comments in your link, I came across a post quoting GM Edmar Mednis:

A move which was invariably given two exclamation marks - 14.Nb1!!
  after the game. May I respectfully suggest that if Spassky had
  proceeded to lose this game it would have read 14.Nb1?? If we look at
  the nature of the position, it should be apparent that neither of
  these extremes is warranted. White has difficulties in how to
  continue, so he decides to first kick Black's Queen. However, this is
  an open position and White's QN is placed well on c3. Retreating it to
  b1 obviously cannot be a winning maneuver. It is simply an interesting
  concept, which works because Fischer has an off game. Under the
  circumstances 14.Nd1!? would also have probably won. As a historical
  note, it may be stated that those commentators who were loudest in
  applauding 14.Nb1!? neither played it themselves nor worried about it
  when their turn came.


598: <p>In <a href="http://www.chessgames.com/perl/chessgame?gid=1044724" rel="noreferrer">game 11 of the 1972 World Championship</a>, Spassky as white moves his Knight back to its <code>14. Nb1</code> starting position. Apparently, this moved was received as <code>14. Nb1!!</code>. But to me, it seems as a simple attack on the invading black queen to flush her out of the zone.</p>

<p>What about this move makes it so interesting?</p>

<p>Shown below is after move <code>13. Kh1 Bd7</code></p>

<pre><code>[FEN "r3kb1r/1p1b1p2/p1nppp1p/8/4PP2/qNN5/P1PQB1PP/R4R1K w - - 0 1"]
</code></pre>
 2001: <p>The idea Nc3-b1 has gradually become well known. In general, the idea is to get the knight to a better square, e.g. the c4 square. Another consequence is that the a1-h8 diagonal opens and can be controlled by the white queen at some point. The third is that the c2-pawn can move forward. In this position, white wants to attack, but has to mobilize the forces first. Nc3-b1 can at first seem to help the black queen to return to c7, where it will be safer. At the same time, the knight can continue with Nb1-a3-c4 and attack the d6 and b6 squares. Another option is to place the c2-pawn on c4 and do Qd2-b2 to control the a1-h8 diagonal. What makes Nc3-b1 special is that it allows white to regroup the forces and then follow up with an attack.</p>
 17: <p>White has completed his development, and Black has not, giving White an advantage. The reason this is true is because of Black's queen moves.</p>

<p>Therefore, the way to prevent Black from completing his development is to harass the queen. When the smoke clears, White will have a clear advantage in development, going into the endgame, making him a heavy favorite. </p>
 307: <p>Taking a look at the comments in your link, I came across a post quoting GM Edmar Mednis:</p>

<blockquote>
  <p>A move which was invariably given two exclamation marks - 14.Nb1!!
  after the game. May I respectfully suggest that if Spassky had
  proceeded to lose this game it would have read 14.Nb1?? If we look at
  the nature of the position, it should be apparent that neither of
  these extremes is warranted. White has difficulties in how to
  continue, so he decides to first kick Black's Queen. However, this is
  an open position and White's QN is placed well on c3. Retreating it to
  b1 obviously cannot be a winning maneuver. It is simply an interesting
  concept, which works because Fischer has an off game. Under the
  circumstances 14.Nd1!? would also have probably won. As a historical
  note, it may be stated that those commentators who were loudest in
  applauding 14.Nb1!? neither played it themselves nor worried about it
  when their turn came.</p>
</blockquote>
