Whats the use of LOST.DIR folder actually? why does is automatically appear after every reboot?
Lost.dir is a system folder. Its a place where the Android OS places files that were recovered during a system boot up.
What is the folder for?
Its quite evident that there is no application named LOST.DIR installed on your device. At times the folder's size can range in gigabytes. In such situations one may wonder about the contents of the folder and its use, and whether it is safe to delete the folder to save memory.
Can I delete the contents of LOST.DIR ?
In order to save precious memory space its completely normal to delete the contents of LOST.DIR as it only acts as a recycle bin. You can also delete the LOST.DIR folder itself but it will reappear the next time the system boots up. When your Android system throws up a message saying 'Preparing external SD card' its actually checking the contents of LOST.DIR, and if it fails to locate the directory, it creates one.