Samsung Galaxy S III (T-Mobile)
Replying to: This phone has a Barometer ? by Tofuchong
If you have a handful of inputs from GPS and Wi-Fi networks, each GPS satellite and Wi-Fi access point is one distance reading, in a three-dimensional space. You need at least three inputs to triangulate your location on land, but you need more more when dealing with three dimensional space, and each additional input makes the reading more accurate. Therefore an input on the height axis helps make the whole calculation more accurate.
Knowing height can also help indoor navigation, which Google now does; are you on floor 2 or 20? etc.