Is it safe to delete lost.dir files to save space in an android cellular phone, or is it better to move it to the sd card?
This question helps explain what it is.
In short, it is similar to the Recycle Bin in Windows. The system sends files that were recovered in during boot to it. When you put an SD card in, the "Preparing SD card" notification is shown when it is checking the LOST.DIR folder.
This folder is safe to delete, just as much as emptying the Recycle Bin on Windows is. But you will see the folder reappear next time you restart your device.