Sheet templates are employed by the Sheet Set Manager and also the Civil 3D Plan Production Tool.
Sheet templates contain Layouts that contain Viewports that allow you to publish and plot Sheets via the Sheet Set Manager.
The Sheet Templates that ship with the Framework products contain a variety of scaled example Layouts that include titleblocks (with Sheet Set Fields).
Both standard Sheet Set Manager Layouts are supplied and specialized Plan Production Tool Layouts with preconfigured Plan and Profile and Pages of Sections viewports included.
Sheet templates may also contain Page Setups and Page Setup Overrides.