Sometimes there is information that only the client is allowed to enter. The support agent can see them but they must NOT be able to change them, typically for legal or regulatory reasons. Let's give a practical example.
An indie developer is publishing applications on the Apple App Store and the Google Play Store. These stores do not provide a help desk feature. The developer does not want to deal with the unmitigated hellscape that's doing support over email for hundreds of people. Instead, they want all their support to go through their site's ticket system.
It sounds like a chicken and egg issue. Luckily, there's a way to implement that with a custom field.
First, install the third party plugin and remember to publish it — it's the Fields - Privacy Checkbox plugin. You do not need to configure it.
Now go to Components, Akeeba Ticket System, Fields. Make sure that the drop–down at the top left reads Tickets and click on thebutton. Use the following information:
Type: Privacy Checkbox (privacycheckbox)
Access: Guest (so it only shows for Guest users)
Click on the Options tab and use the following settings:
Automatic Display: Do not automatically display — This is not strictly necessary. Since the field has Guest access it will not show up for staff and the logged in client anyway. This is just a reminder to you that the field will be invisible.
Next up, click on the Permissions tab. Click on the Guest group. Set the Edit Custom Field Value permission to Allowed.