6824 - All Nexus: What are the differences between the DCS and the PLLREFCS components?
User can use one or the other. In terms of clock path delay, using the PLLREFCS primitive would give a much shorter delay due to its proximity to the PLL as its primary function is to be used for the PLL.
DCS, on the other hand, is located at the center of the device as it needs to be close to the DCS_CMUX and within the same distance through each of the clock regions.