An excellent measure of restriction, which takes the e4-square away from several black pieces, and soon d5 as well.
Fixing a target on a7. We can also notice that the bishop on a8 has turned into a very passive piece.
Now White manages to swap the enemy's active queen. Preferable was 6...Nxf5 7.Qc3 with a clear, though not decisive advantage – Kasparov.