The Dropbox iOS app does not use your device’s location data. However, if you turn on background uploading for camera uploads, the app will ask for permission to access your device’s location services. When background uploading is on, the Dropbox app will periodically upload photos even when the app is closed. There are a few things that trigger background uploading, including changes to your device’s location. This is designed to make camera uploads work more efficiently and does not collect your location information.
Dropbox's background uploading feature uses a low-power version of Apple's location services. If you have a big backlog of photos to upload, you may notice that the app uses some power. But once that's done, uploading new photos should have little effect on battery life.
Understanding iOS Location Services
For information such as how to tell when an app is using location services, steps to reset or change your location settings, and to learn more about iOS location services, see Apple's Understanding Location Services support article.
Apple's API reference
For iOS developers or highly technical readers, check out Apple's Developer documentation to learn more about the API library Dropbox uses to access iPhone and iPad photo galleries.