Hierarchical Design (HD) flows enable you to partition a design into smaller, more manageable modules to be processed independently. The hierarchical design flow involves proper module interface design, constraint definition, floorplanning, and some special commands and design techniques. For more information, see the Vivado Design Suite User Guide: Hierarchical Design (UG905).
Using a modular approach to the hierarchical design lets you analyze modules independent of the rest of the design, and reuse modules in the top-down design. A team of users can iterate on specific sections of a design, achieving timing closure and other design goals, and reuse the results.
There are several Vivado features that enable a hierarchical design approach, such as the synthesis of a logic module outside of the context (OOC) of the top-level design. You can select specific modules, or levels of the design hierarchy, and synthesize them OOC. Module-level constraints can be applied to optimize and validate module performance. The module design checkpoint (DCP) will then be applied during implementation to build the top-level netlist. This method can help reduce top-level synthesis run time, and eliminate re-synthesis of completed modules.