People avoid prototypes for enforcing argument types and argument count because prototypes do not enforce argument types or argument count:

sub foo ($) {
  print ">>$_[0]<<\n";
};

my @bar = (4,5,6);

foo 1,2,3;
foo @bar;
foo(@bar);
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I forgot to point to Tom Christiansens Far More Than You Ever Wanted To Know About Prototypes - it details the uses and abuses of prototypes, and my rule of thumb has been to avoid them unless I really need them.