Continuing in the Yates, Black plays 9...Bg4 and pins the Knight in the Bogoljubov Variation. This move got it's name from the London game between Capablanca and Bogoljubov. The Russian actually played the pin on his 10th move, preferring to trade pawns on d4 first. But it's the same position in the end.
Now White's control of d4 is weakened. The Queen's mobility is also reduced with the light square Bishop on the Queenside. She will have to protect the Knight or Black will trade, doubling pawns and leaving the King vulnerable.
If you have Black you can think about getting your Queen's Knight into an advanced position. Here you can make a nice home on c4 or force the concession of White's Bishop pair. You also want to get those Queenside pawns moving.
With White you are scheming to break the pin and play f4. Hopefully this can support a central advance, putting the squeeze on Black.