[generic-sensor] When to use the new GeolocationSensor API

When would one opt to use the Sensor GeoLocation
<https://www.w3.org/TR/generic-sensor/#background> API as opposed to the
existing standard navigator.geolocation.watchPosition?

Can someone explain the added value of this second API or the use-cases
that can be solved by the sensor API that cannot be handled here
<https://dev.w3.org/geo/api/spec-source.html>?

The Web App world desperately needs a background geolocation capability but
the sensor API architecturally prohibits this.

What is the point of the following redundant interface to geolocation: -

let sensor = new GeolocationSensor({ accuracy: "high" });

sensor.onreading = function(event) {
    var coords = [sensor.latitude, sensor.longitude];
    updateMap(null, coords, sensor.accuracy);};

sensor.onerror = function(error) {
    updateMap(error);};
sensor.start();

If technical merit contributes to W3C/IETF resource allocation surely the
battery efficient background geolocation solution proposed here
<https://drive.google.com/open?id=0B7Rmd3Rn8_hDNW1zSWRoXzBTclU> is what
should be promoted?

How about new ClockSensor({ granularity: "minute"}) ?