I am referring to the fact that, as documented in perlsub, calling &foo shares @_ with the current package. Calling it with parentheses gives it its own argument list. The following demo script may give you an idea what this means:

#! /usr/bin/perl
use strict;
use vars qw($indent);

$indent = '';
print "Here is how things go without an &\n";
demo_no_amp(1..5);
<STDIN>;
print "Here is how they go with an &\n";
demo_with_amp(1..5);
<STDIN>;
print "And with explicit argument passing\n";
demo_explicit_args(1..5);
<STDIN>;
print "Done\n";

sub demo_no_amp {
  local $indent = $indent . "  ";
  while (@_) {
    my $arg = shift;
    print $indent, "Without &, '$arg'\n";
    demo_no_amp();
  }
}

sub demo_with_amp {
  local $indent = $indent . "  ";
  while (@_) {
    my $arg = shift;
    print $indent, "With &, '$arg'\n";
    &demo_with_amp;
  }
}

sub demo_explicit_args {
  local $indent = $indent . "  ";
  while (@_) {
    my $arg = shift;
    print $indent, "With explicit args, '$arg'\n";
    demo_explicit_args(@_);
  }
}
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Puzzle out why those three cases are so different and you will understand why I think the second one is dangerous.