When you attempt to delete a user, you will be prompted with the option to assign the previous issues to a new user. If you opt not to assign the issues to a new user, the previously assigned items will be listed as "unassigned." Optionally, you can disable a user. The user will no longer have access, but items to which they were assigned, will still be assigned. The latter option is used when the record of assignment is needed for historical or archival purposes.