If you want GPS, you need to select high accuracy. Word "usually" for medium and low accuracies mean that we know that those modes can use wifi and cell info, but they can also use some other info (e.g. bluetooth beacons and accelerometer). GPS is only used in high accuracy. Medium and low accuracy modes are intended for saving battery, so those modes never use GPS module.
If you want GPS, you need to select high accuracy. Word "usually" for medium and low accuracies mean that we know that those modes can use wifi and cell info, but they can also use some other info (e.g. bluetooth beacons and accelerometer). GPS is only used in high accuracy. Medium and low accuracy modes are intended for saving battery, so those modes never use GPS module.