Files that begin with a period, "." are intended to be temporary and invisible but many times they don't get cleaned up by your computer and are unsightly in file managers and take up space. iDelete for Android works in the background and will delete these files that are left behind. Make sure you don't have any files that start with a period that you don't want to delete before using. "nomedia" files and files stored in your DCIM (camera) folder will not be deleted while using this program as they are intended to remain on your device.