It might be for correlation with his timing.
But WLM r used in the synthesis part where the net resistance and capacitance is calculated using the WLM table.
By using this RC value the delay of the net is calculated and is used for checking the timing in STA.
If u open the WLM table u will get the idea. As it will say for a specific fanout value what will be the number u need to multiply to the unit resistance and capacitance to get the resulted R and C values.