This feature is typically used when a user leaves the company and another user must take responsibility for customers, prospects and ongoing cases.
In the left column designate the user to switch from. In the right column designat the user who must assume responsibility.
Once the "from user" has been selected the list below shows the number of different items owned by the user. For each of the desired items, then click on the "Change User", which immediately transfers the items to the new ownership.
Completed activities are not transferred. Here it is of course important that you can later see who actually conducted meetings or sent mails.
If users use calendar synchronization with Exchange (Office365), there may be situations where the transferred activities (meetings) no more gets synchronized. This is because there may arise differences in who in Outlook appears as organizer of an activity and the new organizer (owner) in CRM on the same activity. This is a known issue in Exchange / Outlook, where - even without CRM in the picture - it may prove difficult to handle Outlook agreements for an employee who no longer have access.