If you are looking to limit who can add events to workgroup Calendars, there is a way this can be done from the back end. A setting can be changed in the Calendar Module.config file. Please note that this change will affect every workgroup and will limit Managers as the creators and editors of any Calendar events. 

On the web server go to:

1. (Drive letter):\inetpub\wwwroot\(portal folder)\Modules\Calendars
2. Edit the Module.config file 
1. Look or search for the following tag:  <OnlyForManager>false</OnlyForManager>
1. Change 'false' to 'true'. The tag should read as follows:

<OptionPage>
<Text>Add or Change Calendar Event Types</Text>
<FileName>EditEventTypes.aspx</FileName>
<OnlyForManager>true</OnlyForManager>
<Scope>organizationalUnit</Scope>
</OptionPage>
<OptionPage>
<Text>Edit your calendar subscription</Text>
<FileName>SubscribeToCalendar.aspx</FileName>
<OnlyForManager>true</OnlyForManager>
<Scope>organizationalUnit</Scope>
</OptionPage>

    3. Save the file. Now only managers will be able to add/edit Calendar events in all workgroups.