The safest place for the king.

1...0-0?! 2.Rae1 is less appropriate, as Black has a problem with the h4-pawn

Reinforcing the strong blocker on e5.

Preparing 6...Rg8 with a good game.

With the kingside safely blocked the black king is in no danger on g8, whereas the queenside may now be used for an attack.

Taking command of the light squares.

5.e5 Nb6 6.b3 Ne4 7.Nge2 a4 , continuing the attack.

Heading for c4 with a strong initiative.

Preparing a king march to the opposite flank to neutralize White's coming attack.