Approval rules and dimensions enable you to package approval routing criteria together and use them for handling the Assigned Approvers step in the approval steps of your approval process.

If you assign approval responsibilities to a specific user or role, no further logic or criteria can be put into that assignment. The only criteria available for the approval step are the step entry criteria. By associating rules at the assignee step via approval rules, you can dynamically assign approvers based on the same object record information used for the entry criteria.