Why Build Skyscrapers At All?

The tower equals the floorspace all of the blocks on the left

This is why. More or less. As noted by secretrepublic.com, while skyscrapers instead of sprawl has some serious merit, you can lose the feeling of a well proportioned city vertically, just as we currently do horizontally. The urban morphology on display here is quite American, but the point is equally valid. The example also works equally well with say, an 8-10 storey building, as it does this tower.

There is quite literally an infinite amount of space vertically, and a very finite amount of space horizontally. Finding that balance is the job of planners.