in reply to Answer: Can Perl remain persistent for scripts just like mod_perl does for apache?
in thread programs and processes
The /usr/bin/perl executable can take a second to start itself before it even begins to look at the script. That time would be saved.
Also, mod_perl will keep the compiled version of the script in memory so that it doesn't need to be interpreted before running again. If you were to have a large script several thousand lines long, this would save time.
Lastly, since perl is used so much, any time saved each time is lots of time saved overall!