You should be careful using this setting. It used to cause trouble in older versions of mod_perl, and some people still report problems using it. If you are not sure if it's working properly, a full stop and restart of the server will suffice.
Starting with mod_perl Version 1.22, PerlFreshRestart is ignored when mod_perl is compiled as a DSO. But it almost doesn't matter, as mod_perl as a DSO will do a full tear-down (calling perl_destruct( )).