If With Perform As User, you can specify a different user account that owns the necessary permissions. Usually, this user account is assumed to be only technical (impersonation), with broad permissions, but not used to log into a Jira account as a person. If you don't specify anything a user here, the transition on the related will be issue is performed under as the same user , who triggered this post function on the origin issue by default. Thus Therefore that user must have the necessary permissions on the related issue. However, in In some restrictive setup setups, that user might not be allowed to do so have the permissions on the related issue . He or even might not even see have access to the project of the related issue!With 'Perform as User' you can specify a different user account which owns the necessary permissions. Usually this user account is assumed to be only technical (impersonation), with broad permissions, but not used to log into Jira by in life persons.
In combination with the 'User is in Any Users' Condition, you can hide a transition from all other users than the 'Perform As User' user.