220.127.116.11. Avoid Delay Chains in Clock Paths
You require delay chains when you use two or more consecutive nodes with a single fan-in and a single fan-out to cause delay. Inverters are often chained together to add delay. Delay chains are sometimes used to resolve race conditions created by other asynchronous design practices.
In some ASIC designs, delays are used for buffering signals as they are routed around the device. This functionality is not required in FPGA devices because the routing structure provides buffers throughout the device.