What custom fields are shown and when depends on the type of object the custom field is applicable to, and when that object is being used.
Always shown if applicable to the object:
Addresses
Groups
Incoming messages
Interviews
Locations
Projects
Training courses
Training records
VSys Live pages
Shown if the associated job has it as a valid custom field, or if that job's job group has it selected if the job itself doesn't explicitly have 1+ custom fields selected:
Assignments and recurring assignments
Hours records (administratively - VSys One/VSys Anywhere)
Job associations
Job slots
In VSys Live and VSys Live Kiosk the rules are a bit different: when checking out or self-entering hours:
If the job specifies Don't prompt for any custom fields at checkout/hours entry, then no custom fields will be shown.
If the job has one or more Custom fields to prompt for at checkout/hours entry, then only those custom fields will be shown.
If Don't prompt for any custom fields at checkout/hours entry is not checked, and Custom fields to prompt for at checkout/hours entry is blank, then VSys looks to the job's job group:
If the job group specifies Don't prompt for any custom fields at checkout/hours entry, then no custom fields will be shown.
If the job group has one or more Custom fields to prompt for at checkout/hours entry, then only those custom fields will be shown.
If all of these fields are un-checked or blank, then VSys will show all numeric custom fields applicable to the job in the custom field's definition.