If you start a batch script (file) from an already open command window (by typing its name and pressing ENTER), if the batch ends with EXIT, that window will close. Without an EXIT, the window will stay open.
If you start a batch by double clicking it in Windows Explorer, the window will close when the batch ends, whether there is an EXIT or not.
If you follow EXIT with a number, that is the exit code the script will leave behind as an errorlevel.
If you don't need any of this, you can omit EXIT.