Good question.

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Experience tells you, if you can, tuck the King out of the way before you go sac-happy.

Tucking the King out of the way stops any annoying tempo gaining checks and tempo is what it's all about when sac attacking a King.

Looking ahead at possible defensive set-ups you see the bones of this pattern from the above games with Black to play.

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That e7 Bishop is not helping Black but it has a check gaining a tempo for Black to hold his second rank with the Rook. The kind of annoying check I was talking about. In some lines in the actual game Bc5+ may have played a game saving part.

Leaving on or over-looking checks against yourself when sac-attacking is very dodgy and has been the downfall of many a 'this looks good' combination.

You often see the good guys moving their King from c1 to b1 after they have castled queenside. This is to get away from bolt from the blue checks on the open diagonal.... or pins.

I kind of know what I'm talking about here.

G Chandler vs J B Henderson, 1994

That clown Chandler thought he could save a tempo by not playing Kb1 but then again he's not what I would call one of the 'good guys.'

(recently found out that that game appears in one of the Adorjan 'Black is OK' books. Good. I hope someone somewhere learned something about King safety.)

Also Anand, or any attacking player, does not want to keep going over attacking calculation to keep looking at a possible check and what it can do. Black's defensive duty is much harder without a tempo gaining check. (18.Kh1 was a pre-attacking move.)

It's possible Anand had the coming attack on his prep-board before the game and decided or discovered Kh1 needs to be played because as was pointed out in the main Norway Chess thread, the game and sac idea had been seen before 'cept in that game White did not play Kh1. Black got a Queen check in and managed to get the Queens off. (though White still won.)

Anand polished up the attack.

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The idea is 21...Nxe4.

If other things are equal and if White can make his lead in development and greater space count, White has a winning or almost winning positional advantage.

In that case it will be advisable for White to attack, and if then move 16 f5 makes the right choice of attacking move, this will a sound attack as it is based upon a positional advantage and it will be likely to succeed against any defence.

I admit that after the subsequent 22…Bxe4 I did not see the powerful (yet not too surprising) 23. Rg1! which sets up a most annoying check that will cost Black plenty of material.>

There is more to come. After 23 Rg1 black intercedes with 23...Bg5, giving back the bishop, evening the material.

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Now white wins a full piece beginning with 24 Qxg5+ Kh7 25 Qg7+!

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