This is the documentation of JSU for Jira Server/Data Center. If you are using JSU on Jira Cloud, you can find the documentation here.
The 'User Is In Any Users' will verify that the current user is one of the selected users.
You must specify the allowed users, when configuring the check. For example:
For information on how to configure a condition for a workflow transition in JIRA, see the JIRA documentation.
A workflow is configured so that the 'Automation' transition has the 'User Is In Any User' check = 'jsu-technical-user' user only. This is a user account which does not belong to a human person, but is used for all kind of automations. It has more permissions than normal users, so automations can do things which would be restricted for normal users.
A normal user viewing an issue in that workflow will not see the 'Automation' transition.
This is a perfect use-case to hide a Transition which will be triggered by a 'perform as user' (impersonate) Post-Function. So you configure also 'jsu-technical-user' as the 'perform as user' in the Post-Function.
Only the boss
You might restrict some transitions in your workflow to the big boss and his deputy.
However, for such cases you might also consider other conditions like User Is In Any Groups Condition or User Is In Any Roles Condition.