Here's the thing. It's not slower. It's actually faster, but your benchmark wasn't constructed properly. You used a constant, which I think Perl was optimizing away. Also, you were burying sprintf within a relatively expensive function call. Take a look at this: 
use Benchmark qw[cmpthese];

sub one {
        sprintf("%09d",@_);
}

sub two {
        substr("000000000$_[0]",-9);
}

cmpthese(100, {
        one => sub { for(0..10000) { $_ = one($_) } },
        two => sub { for(0..10000) { $_ = two($_) } },
        tre => sub { for(0..10000) { $_ = sprintf("%09d", $_) } },
});

__DATA__
Benchmark: timing 100 iterations of one, tre, two...
       one: 12 wallclock secs (10.63 usr +  0.00 sys = 10.63 CPU) @  9
+.41/s (n=100)
       tre:  3 wallclock secs ( 3.38 usr +  0.00 sys =  3.38 CPU) @ 29
+.59/s (n=100)
       two: 12 wallclock secs (11.08 usr +  0.00 sys = 11.08 CPU) @  9
+.03/s (n=100)
      Rate  two  one  tre
two 9.03/s   --  -4% -69%
one 9.41/s   4%   -- -68%
tre 29.6/s 228% 214%   --

[download]
You're correct in your assumption that substr is faster, so long as the only number you need to process is "213" and you bury it in a subroutine call. You'll have to admit that in the real world users tend to ask for a little more functionality than that.

It would seem that sprintf wins by a knockout.

In reply to Re^3: sprintf vs. substr (for zero-padded values) by tadman
in thread sprintf vs. substr (for zero-padded values) by Theseus

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.