So you do have a problem you're trying to solve: Too much HD usage and it's filling your HD.

The purpose of the System Performance report is to show how much the server is handling at any moment in time. If you run it daily at the same time, the information provided will be pretty much useless as it could randomly hit the busiest part of the hour or the least busy part of the hour.
It sounds like you're not really looking for the data this report shows at all. This report is primarily designed for troubleshooting issues with overload and/or load balancing among servers. It kinda sounds like you're not in need of that sort of data at present. Especially if the ONLY problem your system has is a hard drive that is rapidly filling because of this data! However, you could set the system to prune (delete) this data daily and keep only 24-48 hrs worth of data in case it means something to you.
What information are you hoping to get from this report?