The sap hana administrator will come across the situation where a user account is deactivated. A personal user account could have been deactivated temporary because the person was due to be absent for a while. The day the person comes back his user account need to be activated.
Another good reason would be that a temporary technical user has been created for short requests but would be kept deactivated while not in use.
For instance, temporary administrator user accounts could be given to external people as part of a short-term general database maintenance.
Note: In some cases user password may require to be updated as well as to be activated. Ex: the password validity period is most likely to be out of date if a user has been deactivated for a long time.