In most of my Xilinx FPGA projects I don't bother running post-route simulation, unless I see mysterious malfunctions in the hardware FPGA. The culprit is usually a timing constraint that I applied incorrectly, or a bug in the development tools (I then complain to Xilinx).
P& R simulation are most useful thing if u want to avoid malfunctioning of H/W. As per your design requirment need to give constraints. Always check P&R simulation.