Optimal Image optimizes the photos and videos on your phone in order to free up as much space as possible, without affecting how they look on your device screen. By optimizing the originals in your Camera Roll you could save up to 90% of the space.
Optimal Image does not overwrite or transform your original photos in any way. Instead, an optimized copy of your original will be saved in the album My Optimal Roll, within the app. To save space, simply back up your originals to your computer and delete them from your device.