Let's assume that Tom has to approve all quotes with a discount over 25%, but all managers below Tom also have to approve the quote before Tom does. That is not a problem, unless Tom has different hierarchies below him.
Hierarchy 1: Jim > Bob > Tom
Hierarchy 2: Stacy > Ashley > Jess > Tom
If you create two steps in the approval process (Assigned: Manager and User: Tom), then the approval process will skip Jess. How do you create an approval process that makes sure each manager is involved without needing to create a step for each level of the hierarchy? If Stacy becomes an approver for someone below her then the approval process would need another step added, and that is not very flexible.