I bought a house with a sunken living and wanted to raise the floor. We used blocks of this stuff to fill up the sunken living room, so we only had to use 6" of concrete on top. I was surprised when I found out, but my builder says it is common.

I don't know if I would use this stuff outdoors, though. We had a bean bag chair full of polystyrene balls leak outside, and I was finding the stuff in my yard for years.