Territory management versus role hierarchy
Key Takeaway
Keep management lines in the role hierarchy and let the territory hierarchy extend access. The access from Sales Territories rolls up to the role hierarchy, so copying the territory structure into the sales branch of the role hierarchy is unnecessary.
The role hierarchy and the territory hierarchy are two ways to give users wider access to records, but they model different things. The role hierarchy fits management lines, and Sales Territories can model matrix coverage, where someone reports to multiple managers. The two hierarchies are meant to complement each other, not duplicate each other.
What the role hierarchy does
Record access starts with organization-wide defaults, which lock data to the most restrictive level. The role hierarchy is the first way to open access wider. Users higher in the hierarchy can always access the same data as users below them, regardless of the organization-wide defaults.
Role hierarchies only give more users access to records, so they can't be stricter than your organization-wide defaults.
Roles primarily control record-level access through the role hierarchy and sharing rules. Object and field access is a different job that is easy to confuse with roles: it comes from profiles and permission sets.
A role can also represent a level of data access that users need, rather than matching your org chart.