From perlsub. To call subroutines:

   1. NAME(LIST); # & is optional with parentheses.
   2. NAME LIST; # Parentheses optional if predeclared/imported.
   3. &NAME(LIST); # Circumvent prototypes.
   4. &NAME; # Makes current @_ visible to called subroutine.
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Personaly I prefer to use NAME(LIST); and prefix & only in special cases like &$code.