What is app data and what are the consequences of deleting it from my device?

App data is the data that is downloaded or generated as part of a device’s content - for instance, downloaded books or music, while cache files are temporary files many programs generate while in use, such as saved portions of websites you visit in a browser. 

CCleaner for Android identifies app data that you should be able to safely remove from your device. When using this feature, consider the impact that removing app data may have on the functionality of the source app. 

For example, each time you open Google Maps, the app re-downloads any offline maps that were removed by CCleaner Android. Similarly, Spotify re-downloads offline tracks when needed. Conversely, deleting OBB type app data, which is often associated with large games, may release a lot of space on your device while allowing you to keep the game, but, you may need to reinstall or re-download the OBB file if you decide to continue playing in the future.

Some apps also keep their settings in the app data, so it is possible that you may need to set your preferred settings again or log back in after cleaning this data.