What's the use of that?

Seems kind of boring for the people in the pool.
There should be some chairs and tables, maybe a coffee shop.

I have also seen the variant where the pool was something like a meter and a half deep, so that the people on the floor below could look up at the people swimming above them, and the swimmers could look down at the people below through the glass bottom (which must be rather strong to hold the weight of the water!).

The next would be a pool at a the edge of a skyscraper roof, with an overhang so that the swimmers could look down through a glass bottom, watching traffic a hundred meters below...