This prevents a user from having to enter the Y each time the command is executed. The last part of the line is the actual command to delete all files in the temporary subdirectory. Incidentally, line 3 is a neat little trick to use either in batch files or from the DOS prompt. Many commands requiring a response can be dealt with using ECHO and the piping symbol. If you don't set a TEMP subdirectory, it usually defaults to the Windows subdirectory.
Some applications actually have problems if there are other files in the TEMP subdirectory.
Your particular files were created using Windows Write. These files are normally deleted by Windows upon exit. The presence of temporary files could indicate logical damage to the drive since the same conditions that leave temporary files on the drive also leave open files. The system keeps track of where the pages are located. Windows will generate GPF's when it detects logical damage to the hard drive.