Dropbox Carousel allows you to backup photos and videos, share them with other people in the world and much more. It displays photos and videos stored on your device as well as the photos and videos saved in your Dropbox. If you download Dropbox Carousel app on your device and already have photos in your Dropbox, then Carousel will not download your photos to your mobile device. It will only display those photos when you open the Dropbox Carousel app.
If you turn ON Carousel Backup, then photos and videos on your mobile device will automatically backed up to your Dropbox account. If the photos are already in your Dropbox, they will not backed up. Once you have backed up photos and videos to Dropbox, you can access them from anywhere on any device with an internet connection.
Note: The storing thumbnails of your photos may take up a small amount of space on your device. The amount of space taken up is directly related to the number of photos in your Dropbox.