This thread covers same question:
SnapMirror relationship events: (The ones you can configure)
As suggested in the thread, if there is any lag-event for a particular 'svm:volume' relationship, then that is an indication to bring your attention to the issue (possibly lag). Basically, it is designed to inform you on the events that needs your attention.
If you would like to schedule reports for 'how relationships are doing', then you can go to:
Volume relationships tab in the OCUM GUI and you should be able to see "how all your relationships are doing" - All green means that's great. On the top there is 'view & schedule report' that would allow you send the list of all relationships performance until the of the report generated to the mail-recipients you have given in the scheduled report.