Not the most favoured move, but a perfectly natural developing one, and consequently it cannot be bad.

4 ........ P × P

P - Q B 4 is generally played in this case instead of the text move.

5. Kt × P Q Kt - Q 2
6. Kt × Kt ch Kt × Kt
7. Kt - B 3 B - K 2

8. Q - K 2

This is played to prevent P - Q Kt 3, followed by B - Kt 2, which is the general form of development for Black in this variation. If Black now plays 8...P - Q Kt 3; 9. B - Kt 5 ch, B - Q 2; 10. Kt - K 5 and White obtains a considerable advantage in position.

8. ........ O - O
9. B - K Kt 5 P - K R 3

Of course Black could not play P - Q Kt 3 because of B × Kt, followed by Q - K 4.