Helps to reduce spam
I recently tried to enhance spam assassin with a free Cloudmark Authority anti-spam client (apparently most of UK ISPs like VirginMedia, Plusnet, TalkTalk use it) and so far it blocks around 25-30% extra spam comparing to spam-assassin alone.
I run a small tech company with a postfix MTA and I had a lot of spam before with spam assassin. I've also tried to short-circuit spam assassin whilst using Cloudmark filter and it delivers good 10-11x times faster performance and processing.
Another handy feature is the fact that Cloudmark Authority lets you to mark spam messages from the webmail client enabling the system to learn dynamically. Postfix integration all seemed to be pretty simple as well.