Many designs consist of parts that run at different clock rates. The fastest part uses the system clock period.
For the remaining parts, the clock period is an integer multiple of the system clock period. It is important that downstream tools know what speed each part of the design must achieve. With this information, the efficiency and effectiveness of the tools increase greatly, resulting in compilation time reduction and improved hardware realizations. Multicycle path constraints in the constraints file specify how to divide the design into parts and set the required speed for each part.