Rule subjects are an optional component that enable an administrator to apply an additional level of criteria beyond the straight approval rule. For example, if you had an approval rule that stated approval was needed for any transaction over $200, you could further define it by using a supplier subject that states the rule will apply to any transaction over $200 from specific suppliers.
It is possible to use the following additional criteria for an approval rule:
Subjects are used to create a more specialized approval workflow which makes it easier to focus and report on specific areas of your organization's indirect expenses.