The biggest reason to use it is if you are trying to be efficient with vacation passes. You can use it to create a reservation with as long as a 24 hour layover somewhere and as long as you keep it all on one reservation, it only uses one vacation pass.... We've used it to take an early flight to SFO, spend the entire day there, then the late flight to SYD. The custom routing let us keep it on one reservation and use only 1 vacation pass. If just type in XYZ outstation to SYD the early flight from the outstation to SFO wouldn't show up because it was a 12 hour connection.