For whom? Carerix users that have used Calendar 1.0 without a sync to Outlook/Google.
Why? So you can, temporarily, look up meetings that only exist in Carerix Agenda 1.0. You can use your new Calendar creating new meeting.
How? Administrators can activate "Show old Calendar" at Marketplace Settings, at Maintenance menu. Activation is on Application level (and not per individual user)
When you start using the New Calendar, you can still access your old version for limited times. This way you can still look up your 'old' Calendar and see events that were never synced to Google/Outlook.
If you want to create new meetings, go to your new Calendar!