As with any situation where you're including external code in your production code base you have to evaluate what it contributes and what the pros and cons are of including said code. But from the perspective you're speaking (
, no?) I personally don't think this is an issue. Most code from the likes of CPAN is heavily tested and will hopefully have thought of most of the things that you won't have if you were to have re-written the necessary code yourself. To re-write what you need will probably take far longer as a lot of the code on CPAN has had quite a few man hours behind them and are quite often written for a specific purpose by people who know the ins and outs of the problem space. The issue of speed is really a bit of a premature optimisation as generally the bloat of a module is the amount of code, which if you're only using a small amount is a non-issue as the only penalty you'll incur is the compile-time parsing. Of course this is not to say include every module, all and sundry, for every piece of code that could use a module, just to say that far more often than not the excuse of speed when including CPAN type code isn't an issue.