Win32::Sleep just gives you better granuality, and, for certain, takes away portability. Time::HiRes is much more portable in this.

Fairly safe to say that they both 'hand off' the cpu for the duration. The benchmark as run proves little else of course. I'll leave comparing their efficiency/accuracy AAEFTR.

#! perl -w
use strict;
use Win32;
use Benchmark;

timethese (  100, {
    'Win32'    => ' sleep 1',
    'Std'    => ' Win32::Sleep 1000' ,
} );
__DATA__
# output
C:\test>183845
Benchmark: timing 100 iterations of Std, Win32...
       Std: 100 wallclock secs ( 0.00 usr +  0.00 sys =  0.00 CPU)
            (warning: too few iterations for a reliable count)
     Win32: 100 wallclock secs ( 0.00 usr +  0.00 sys =  0.00 CPU)
            (warning: too few iterations for a reliable count)
[download]

A quick 'deco' at the task manager whilst either sleep is in 'progress' shows that they are fairly obviously doing 'nothing'! :^)