Various events are (can be) logged to a file. To manage the file size of the event log you can set its maximum size. If the maximum is reached it will automatically roll over if the backup log file box is checked.
One very handy feature of this is logging cookie exchange when cookie processing is enabled and you are having troubles connecting to complex sites such as hotmail. In this case you will find they use various sites for their service and many will need to have the cookies enabled for several sites.
