Do we need a separate Teams Governance Plan and SharePoint Governance Plan?

Your Teams Governance Plan and SharePoint Governance Plan are separate but complementary governing documents under an overarching Office 365 Governance Plan. While these are two separate tools within the Office 365 suite, Teams utilizes SharePoint as well as other Office 365 components such as One Drive for Business, and Exchange Online to manage Teams content. Teams governance must therefore, align with governance plans for those applications.

For example, SharePoint Governance focuses on site life cycle and management, Teams Governance focuses on the items mentioned in (previous FAQ) Microsoft Teams Governance best practices (i.e., Teams life cycles, naming standards, access, as well as data security and compliance. SharePoint sites provisioned through the Teams creation process, must still comply with SharePoint governance requirements.