^^ Well its not that much of a con now. But it affects anti-aliasing performance in shader heavy titles as a full ROP is disabled along with a 64 bit memory controller.
But there's a plus side as well. In future, if txaa becomes as popular as fxaa, then we can see aa techniques do away with utilizing large memory bandwidth and a shorter bus with less bandwidth will matter relatively less.
So this move was necessary to bring the 660-ti's price level a hundred dollars down compared to a 670 but keeping the no. of sp's intact.
No problems in fullhd gaming and that is where this card is targetted.