When working on a multi-team project, it is convenient to create individual constraint files for each major block of the top-level design. Each of these blocks is usually developed and validated separately before the final integration into one or many top-level designs.
The block-level constraints must be developed independently from the top-level constraints, and must be as generic as possible so that they can be used in various contexts. In addition, these constraints must not affect any logic that is beyond the block boundaries.
When implementing a sub-block it is desirable to have the full clocking network included in timing analysis to ensure accurate skew and clock domain crossing analysis. This might require an HDL wrapper containing the clocking components and an additional constraint file to replicate top level clocking constraints. It is used only in the timing validation of the submodule.
For more information on constraints scoping as well as rules, guidelines, and mechanisms for loading the block-level constraints into the top-level design, see this link in the Vivado Design Suite User Guide: Using Constraints (UG903).