This option is available only for administrator accounts and all contained options are included also in Calendar Settings for each individual user.
The only difference is that these options are used as default values for any user who did not save his/her own Calendar Settings or for any newly created user.
Additionally, you can specify different default Calendar Settings for each Virtual Host. Only choose a Virtual Host you want to modify in a pull-down menu and change whatever you want.
See Calendar Options chapter for details about meaning of the options.