Yes, having the option to enter RTH(fail safe) mode with the S1 switch is a MUST. I use it at the very beginning of each flight just to verify that the phantom has good GPS loock and the compass is working properly. Take it about 30 feet away, switch the S1 all the way down to make sure it correctly returns back to the home location , if not I can just switch back to Attitude mode, bring it back manually for landing and re-calibration.
By testing the return to home function while still in range to take back control if needed I can then just enjoy the rest of my flight without worry that it will indeed return to home if connection is lost.