The prototype is ignored when & is used.

use strict;
use warnings;

sub testing(\@) {
   my ($arg) = @_;
   print("First argument: ", $arg, "\n");
   $arg->[5] = 'e';
}

my @a = qw( a b c d );

print("Test 1:\n");
testing(@a);
print("\n");

print("Test 2:\n");
&testing(@a);
print("\n");

__END__
output
======
Test 1:
First argument: ARRAY(0x1ab2780)

Test 2:
First argument: a
Can't use string ("a") as an ARRAY ref while "strict refs" in use at !
+.pl line 8
.
[download]

It also varies the behaviour of function calls with no parens:

sub testing {
   print("[@_]\n");
}

sub test1 {
   testing;
}

sub test2 {
   &testing;
}

print("Test 1:\n");
test1();
print("\n");

print("Test 2:\n");
test2('moooo');
print("\n");

__END__
output
======
Test 1:
[]

Test 2:
[moooo]
[download]