关于Estimated I/O Latency的问题

To account for clock network latency in external delays, you can set the
estimate_io_latency variable to true. When this variable is set to true, the tool assigns
clock network delay to every input or output port. The tool assumes that clock tree synthesis
balances network latency across different clocks. Based on this assumption, the tool
estimates off-chip clock latency with reference to the synthesized clock tree in the current
design.
If you used the -network_latency_included option with the set_input_delay command
or set_output_delay command, the tool does not use an estimated I/O latency. Using the
-network_latency_included option tells the tool that the clock network latency of the
related clock is included in the input or output delay. The ideal way to model external network latency is to add the delay to the external delay and use the -network_latency_included
option. Using the estimate_io_latency variable gives a reasonable representation if the
clock network latency is balanced across different clocks.
大家是怎么理解上述解释的，我没怎么理解。望高手赐教

一般不用 ，因为pr之前你不清楚 clock network delay多少，你怎么include呢