There are only two instances where there is a need to clean the cache. The first one is if your Android device has very little free space. In which case, you will get a notification on your device about this. You generally don't need to manually check to see how much free space there is.
The second case, is if an app's cache gets corrupted. When this happens, the app may have issues or not even launch. This can be fixed by cleaning the cache of that specific app.
