The entire point of rsync is to send only changes. Therefore once your mirror initially syncs the old versions of modules is not the issue. Indeed, removing the old versions would present additional burden on synchronization! The ongoing burden is the ever-growing CPAN.
The danger in a CPAN::Mini and in removing old versions is that one is assuming that the latest and greatest is the one to use. This is false. Take the case of someone running old software. I personally support systems still running Informix Dyanmic Server 7.31 as well as systems running the latest IDS 11.5 build. We have Perl code that talks to IDS. If DBD::Informix withdrew support for IDS 7.31 I would need both the last version that supported it as well as the current. I can get away with upgrading Perl, maybe, but to upgrade the dbms is much more problematic (license, for one thing; SQL changes another).
