Far too many problems on systems and by extension networks are caused by simple lack of disk availability. Many processes will die or fail to operate correctly if sufficient disk space is not at hand. Constantly checking disk space on a large number of systems is not an option, especially if you're a lazy git like myself :)
Spacewatcher was born to solve this problem. You run it from cron every however often you want. I run it every 10 minutes because its hit is minimal. You set thresholds for your partitions in the script and when the amount of disk space used exceeds these partitions, it whines at you.