Mostly a tool for coders, this one.
Mostly a tool for coders, this one. Its a separate log intended for events where you don't need a permanent record. So you can add debugging entries which write to the rolling log, for example - useful for those situations where echoing variables to the web page would cause problems.
Some anomalies detected by the core code also write to the rolling log - for example, combinations of values which shouldn't occur (and might therefore indicate a hacking attempt).
The rolling log can be enabled on the options page of the System Logs - and you can determine how long events are kept for. I find 7 days to be a good value to use - events are auto-deleted after this time, so your log won't grow for ever.