As the manual page would have told you, exit and
exit 0 are the same. The difference between
exit 0 and exit 1 is that the former
makes that the program has an exit value of 0, and the
latter an exit value of 1.
The convention is that an exit value of 0
indicates the program ran succesfully, while an exit
value other than 0 means an error of some kind occurred.