While not directly related to your example there is a case when you need to declare a sub before you use it and it involves the use of parens. (Assuming the use of strict and warnings). 
#!/usr/bin/perl

use strict;
use warnings;

my_sub();   # works
# my_sub;   # fails "Bareword not allowed..."

print qq{done};

sub my_sub { print qq{here\n} };

[download]
If you declare the sub first 
#!/usr/bin/perl

use strict;
use warnings;

sub my_sub { print qq{here\n} };

my_sub();   # works
my_sub;     # now works too

print qq{done};

[download]
you can now use the sub without parens.

I reckon a good bet, in these circumstances, is to always use the parens.

In reply to Re: subroutine is confusing by wfsp
in thread subroutine is confusing by Abhisek

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