If you have many users in your workgroup that you wish to share calendars with, you may want to configure one of the iCloud accounts as the master where all of the shared calendars are hosted. This will simplify the setup and maintenance of the shared calendars and designate one user as the owner and administrator of the shared calendars.
In the example above, John is hosting all of the shared calendars on his account and is sharing the calendars with Fred, Dave and Mary.
If you need to share calendars in a workgroup where some users use iCloud and some do not, you can setup a hybrid workflow where you are sharing calendars with others through iCloud and over a LAN.