The Kontact Summary View lists events from all calendars you have set up/subscribed to.
This is a sensible default, but sometimes one has subscribed to certain calendars, e.g. Public Holidays (might even be additionally of other countries/regions) or public event lists that you neither want nor need in the summary.
In these cases it would be useful to have a configurable option to limit the summary view to certain calendars / or exclude events from certain calendars. Currently you can only exclude certain event types, but not complete subscribed calendars.