If the system uses a repeater, you need only put the OUTPUT as your freq,.. if it is just a base and mobile simplex/duplex system, then you need both INPUT, and OUTPUTs.
Example:
159.5350 MHz input, and 155.4300 MHz is the output with the type listed as RM (repeater and mobiles) All you need is 155.4300.
155.4300 As output, 155.3100 as input type BM (Base, and mobiles) then you might need both
45.1400 As Base only (dispatch), 45.2600 as mobiles, then you need both.
Hope that helps