It is an urgent and essential requirement to be able to change owners on tasks or projects or assign additional temporary owners. Even better would be an out-of-office deferment to another user, making them the owner of all your work until you switch it off.
As the name implies, this is so that when a user with an active workload is out-of-office or otherwise unavailable (sick/maternity/annual leave) their work can continue to be actioned as usual without interim workflow changes affecting multiple people. Currently, to do this everyone associated with the task must remember to @ the person covering in comments, add them as an assignee or assign them manually as a reviewer, which is unwieldy and open to many human errors.