The case analysis command is commonly used to describe a functional mode in the design by setting constants in the logic like what configuration registers do. It can be applied to input ports, nets, hierarchical pins, or leaf cell input pins. The constant value propagates through the logic and turns off the analysis on any path that can never be active. The effect is similar to how the false path exception works.
The most common example is to set a multiplexer select pin to 0 or 1 to only allow
one of the two multiplexer inputs to propagate through. The following example turns off
the analysis on the paths through the mux/S and mux/I1 pins:
set_case_analysis 0 [get_pins mux/S]