The only reason I can think of it to avoid the extension installation, but then it goes on to use another extension for a function that's available in PostGIS,

The only reason I can think of it to avoid the extension installation, but then it goes on to use another extension for a function that's available in PostGIS, along with everything else. So yeah maybe if you only need to store the data and don't need operations (why even bother then), otherwise just use postgis.