You will also see it often among players rated 1900 to 2700+ and such also rans as Kasparov and Fischer.

The Sicilian is a great opening, but I can see why it might be hard to logically understand its usefulness, since it doesn't occupy the center. Statistics don't lie, however, and there are a great many set ups that are potentially difficult and even deadly for white if he doesn't play it careful.

The Sicilian is a very aggressive Opening - hardly a defence at all really, as it's motive is counterattack.

The Sicilian offers Black more winning chances than any response to e4.

I think Bb5 is better for white here?

The main move is 4.d4. Also 4.Bb5 seems better than this.

Both moves are more proactive. I like d4 better of the two.

Possibly White is aiming for a sort of 'Closed Sicilian'. Which it will be will depend on what the d-pawn does in the next move or so. The game can still transpose into an Open Sicilian (d4), but one in which White has developed fairly conservatively.

After Bb5, the logical anwer for black is a6, after which white cannot retreat to a4 because of b5 and c4, losing the piece for two pawns. The other choice is BxNc6, losing a good and active bishop for a knight, while the central squares it defend are well covered with pawns. If white plans d4 after the exchange, black can still exchange it. After Nxd4, c6 is easy to defend.

A thematic outcome in the Sicilian.

It's also fine to smash the center open immediatly with 5.d4. White's not in danger.

There are no "absolute rules" in chess. This move is not bad, but it is not necessary right now.

This is quite common in the Sicilian (1.e4 c5).

the small pawn center is very mobile and flexible, either bishop can be opened up easily.

The whole concept behind the d6 e6 set up is that either pawn can advance in a variety of white set-ups. 5...e6 is fine. 5...g6, fianchettoing and setting up a classical dragon, is good too.

I would develop with 6.d4, but this is also OK.

I always put my bishop on the outside of the pawn first.

I find that putting the bishop outside the pawn chain in a closed Sicilian doesn't work well if White has a Knight on c3. Black picks up too many tempi with his thematic queenside pawnstorm. If White desires to play Bc4 in a closed Sicilian, it works much better to play the bishop pawn to c3 and transfer the queen knight to the kingside via d2, f1, and then g3 or e3 as circumstances dictate.

The knight isn't doing much on b4, so this is just a waste of time.

I think I would let the c6-N get as many strange ideas about b4 as it likes. Then a3 sends it scuttling back home. White's problem here is to find a plan. One possibility is to accept the loss of a tempo and play the pawn break 7.d4 to open up the game. Another is to bring the c1-B out. 7.Be3!? is playable, as 7...Ng4 8.Bf4 leaves the Black knight looking a bit lost.

I would develop more actively as white, e.g. 8.Be3.

8.Be3 would be met with ...Ng4

See my previous remark. The bishop moves again after ...Ng4, and then what's the knight to do, poor thing?

Yep. In either form of the sicilian (Open or Closed), White can count on Black looking to counter-attack on the Q-side.

I think ...d5 is a fine alternative here give whites passive play.

This seems weaker than just ...d5.

If black pushed a pawn to d5, then white could move the dark square bishop to g5 and take out the knight supporting the pawn push.

Now Nd4 makes some sense. White cannot exchange it due to the fork.

But White could have done better, by the look of it, with the sequence that would have discouraged me from playing 11...d5?! : 12.bxc5! and if 12...Bxc5? 13.Na4! winning material. So the pawn stays on c5: 12...Qc7 13.exd5 exd4 14.d4.

In the exchange sequence up to move 14, White could still profitably have played bxc5.

Black can still break with ...a5 should the opportunity present itself. On the whole, I prefer Black, here, but there isn't much in it.

At this point, white having played weakly, Black is very slightly better.

All the fuzz on queenside just to block it like that... now, who has the best piece setting for a kingside attack? None, I would say, but black has to relocate more piece than white, since the knight and the queen are more or less out of the game. But white has it not easy, too.

A good move to prevent Qc2, attacking h7. It is a very complex position, indeed, since the attack from any side is far.

Rb2 could have saved a tempo for rooks doubling, later, but it is hard to say.