This app needs "SD Maid - System Cleaning Tool" to be INSTALLED! It unlocks the "Pro" status in the free version, enabling all additional features.
SD Maid is a powerful tool. USE AT OWN RISK!
Nobody is perfect and Android neither.
Apps you have already deleted sometimes leave data behind.
The system constantly creates logs, crash reports and debug files you don't really need.
Your SD-card is collecting files and directories you don't recognize.
Lets not go on here...
Why not get a maid to clean it all up?
SD Maid will help you keep your device neat, clean and tidy :-)!
Give it a try, you won't find a more thorough cleaning tool!
Please see SD Maid - System Cleaner for further information!