I knew you were going to ask that.
We have a handful of servers that are close to the thresholds (I'm using 10% for warning and 5% for error). If there is some activity or process that runs on this box, it might, for example, create temporary files that cause the server to drop below the threshold. However, when the process is complete and the files are erased, the free space is now above the threshold. If there was a way for me to configure the alert so that it only notifies me if/when the free space drops below the threshold for, say, an hour, that would stop the up/down messages that I get only a few minutes apart.