The shared user is because multiple people can’t be auto-assigned to a ticket or workflow at a time.

[koteswararao]

The shared user is because multiple people can’t be auto-assigned to a ticket or workflow at a time. we’re going to create a generic user for requests to auto-assign to, they will receive the auto-generated JIRA email, and then will log into the application with the share user and manage the ticket. Does that make sense?

[Nic Brough -Adaptavist-]

Do not do that.  Assigning a generic user will mean you don't know who is the actual assignees, and I can guarantee you that will hurt you in the log run.  It breaks your audit system and (technically, although generally ignored) breaches your licence.