Revoke access removes the access directly from Jira. Depending on how the access was granted, this could mean removing the user from a project role or from a group.
Create remediation ticket doesn't change the access immediately. Instead, it creates a Jira or JSM ticket so someone can review the issue and take action.
Use Revoke when you're sure the access should be removed. Use a ticket when someone else needs to review or approve the change, or when you want to keep a record of the decision.
