I wouldn't make such statements when brother merlyn is around. ;-)

The difference is a big one. An array slice (which is what @arr[0] is) provides a list context, whereas an array element provides a scalar context. For a graphic illustration, try this code:

my @d = qw(this is a plain array);
my @a;
$a[0] = @d;
print "The scalar got '$a[0]'\n";
@a[0] = @d;
print "But the array slice got '$a[0]'\n";
[download]

Many things in Perl will behave differently in scalar versus list context. If you continue to use @a[0] when you mean $a[0], you will have a surprise one day.

OTOH, it's your code....