Uses background location monitoring to create a low resolution GPX file for the entire day. Due to the background location monitoring this uses minimal battery.
This GPX file then be imported into other programmes to provide location information, which is useful for things such as adding GPS coordinates to photos.
No data is exported from the app, other than optionally to iCloud drive.
The background location tracking is much less accurate than GPS as it uses a combination wifi & cellular location rather than GPS. It also only updates every 5min or 500m, whichever is longer. This results in DailyGPX only using a small amount of battery, but does mean that the track is only an approximate location.