If you import bookings from a calendar that is also using ical export, (2 way connection) you will probably create duplicate bookings as they are passed back and forth between the systems.
The '''skip duplicates''' options will not import a booking from the iCal if a non cancelled booking already exists in the same room for the same dates regardless of the source of the booking. For example a booking might be made on your booking page and exported via iCal to a third party system. If using a skip duplicates option, iCal import will not re-import that booking. Note that only the dates are used to determine a duplicate, this means a booking will not import from ical if a booking for the exact same dates already exists in the room, even if it is in reality a different booking.
See the instructions for ical export -> "Data Options" to prevent re-exporting bookings which have been imported by the iCal import channel.