Excessive Sharpness

Continuing with Smyslov's Sparklers, the Gruenfeld Defense, Smyslov Variation was used in the Euwe - Smyslov game, played in the 24th and last round of the 1948 World Championship tournament. The opening moves were 1.d4 Nf6 2.c4 g6 3.Nc3 d5 4.Nf3 Bg7 5.Qb3 dxc4 6.Qxc4 O-O 7.e4 Bg4 8.Be3 Nfd7 9.Qb3 Nb6, when Euwe played 10.a4. Kasparov noted that it was 'The continuation of a theoretical duel. The game Keres - Smyslov (12th round) went 10.Rd1 e5?! [...] with equality. Modern theory begins with 10...Nc6.'

The position after the moves 10.Rd1 Nc6 11.d5 Ne5 12.Be2 Nxf3+ 13.gxf3 Bh5, is shown in the diagram. Kasparov remarked, 'This key position was actively tested over the course of many years but in the 1990s it almost went out of use: possibly players began avoiding it on account of its excessive sharpness.'

(After 13...Bg4-h5)

Since the position doesn't look particularly sharp, I decided to investigate further. The early games using the variation used continuations like 14.f4, 14.a4, and 14.h4. For example, the move 14.h4 was used in the 11th game of the 1958 Smyslov - Botvinnik World Championship match.

In the 1970s, the move 14.Rg1 became popular. The idea is that White will continue Rg1-g3, shielding the h-Pawn from attack along the diagonal and preparing to 'castle on foot'. After 14...Qd7 15.Rg3, Black has the choice of two Pawn breaks, both leading to a sharp game:

• 15...c6 16.dxc6 Qxc6 17.Nb5 Rfc8 18.Nxa7 Rxa7 19.Bxb6 Raa8, and now 20.Bd4 or 20.Rg5.
  
  
• 15...f5 16.d6+ Kh8 17.dxc7 Qxc7 18.Nb5 Qb8 19.exf5 Rxf5, followed by 20.Nxa7 or 20.Nd4.

Black can try other Queen moves like 14...Qc8, but these also become sharp, e.g. 15.Rg3 c6 16.a4. The sequence 16.dxc6 Qxc6 transposes to the first line above.

Why would top players avoid a sharp line? I suppose that some killer defect was found, but I didn't manage to confirm this.