user11518: I'm a mid-level player just starting to systematically study openings, and I'm wondering why it is that after the signature Yugoslav initiation 6. Be3 by White, and the certain follow-up 6. ... Bg7, it seems that virtually all masters (~95% according to lichess) opt to play 7. f3.
Specifically, I've been reading John Emms' Starting Out series on the Sicilian, and the only mention he gives of this move is that it prevents an "annoying Ng4." Why is it all that annoying? For example, let's say I play 7. Qd2 first, then Ng4 by Black, chasing the bishop to g5 for fear of exchange, with h6 by Black forcing Bh4:
rnbqk2r/pp2ppb1/3p2pp/8/3NP1nB/2N5/PPPQ1PPP/R3KB1R b KQkq - 1 9

Sure, the bishop has had some cardio in the opening, and it no longer looks like the typical Yugoslav exchange of Dragon bishops is going to happen, but it at least looks playable. Stockfish 25ply rates it at +0.3. This is equivalent to how it rates the orthodox Yugoslav tabiya:
r2q1rk1/pp1bppbp/2np1np1/8/2BNP3/2N1BP2/PPPQ2PP/2KR3R b - - 6 10

What am I missing?

user7534: F3 prepares g4 and h4, starting a pawn storm on the black king. It also prevents Ng4 by black, harassing white's dark squared bishop.

user4588: Objectively speaking, you're probably right: 7.Qd2 seems fine and after 7....Ng4 white can still hope for an advantage after 8.Bg5 Nc6 9.Nb3.
However, after 7.Qd2 Nc6, black does threaten Ng4. So, white should play 8.f3 anyway, also because it is part of his plan. As a result, we transposed to the main line of 7.f3.
Therefore, white doesn't gain anything by playing 7.Qd2 first. Actually, it only gives black an extra option: 7....Ng4.

11518: <p>I'm a mid-level player just starting to systematically study openings, and I'm wondering why it is that after the signature Yugoslav initiation 6. Be3 by White, and the certain follow-up 6. ... Bg7, it seems that virtually all masters (~95% according to lichess) opt to play 7. f3.</p>

<p>Specifically, I've been reading John Emms' <em>Starting Out</em> series on the Sicilian, and the only mention he gives of this move is that it prevents an "annoying Ng4." Why is it all that annoying? For example, let's say I play 7. Qd2 first, then Ng4 by Black, chasing the bishop to g5 for fear of exchange, with h6 by Black forcing Bh4:</p>

<pre><code>rnbqk2r/pp2ppb1/3p2pp/8/3NP1nB/2N5/PPPQ1PPP/R3KB1R b KQkq - 1 9
</code></pre>

<p>Sure, the bishop has had some cardio in the opening, and it no longer looks like the typical Yugoslav exchange of Dragon bishops is going to happen, but it at least looks playable. Stockfish 25ply rates it at +0.3. This is equivalent to how it rates the orthodox Yugoslav tabiya:</p>

<pre><code>r2q1rk1/pp1bppbp/2np1np1/8/2BNP3/2N1BP2/PPPQ2PP/2KR3R b - - 6 10
</code></pre>

<p>What am I missing?</p>
 7534: <p>F3 prepares g4 and h4, starting a pawn storm on the black king. It also prevents Ng4 by black, harassing white's dark squared bishop.</p>
 4588: <p>Objectively speaking, you're probably right: 7.Qd2 seems fine and after 7....Ng4 white can still hope for an advantage after 8.Bg5 Nc6 9.Nb3.</p>

<p>However, after 7.Qd2 Nc6, black does threaten Ng4. So, white should play 8.f3 anyway, also because it is part of his plan. As a result, we transposed to the main line of 7.f3.</p>

<p>Therefore, white doesn't gain anything by playing 7.Qd2 first. Actually, it only gives black an extra option: 7....Ng4.</p>
