They mostly don't really use actual GPS. Instead they use AGPS [1] tech that uses nearby hotspots, cellar signal triangulation etc. to get your location.
And can you disable it when unneeded (i.e. "99%" of the time) - like you would with GPS (not only because of consumption)?
According to the provided page, Assisted GNSS only works through an Internet connection - to connect to servers that provide cached GPS data. Triangulation comes from other technologies.
[1] https://en.wikipedia.org/wiki/Assisted_GNSS