The single channel will flare and land the aircraft because it all is done on RA at the end. It is mentioned in the tech manual.
Very useful if you were in the unfortunate position of taking off in low vis (with only the suitable Cat 1 return alternate max allowable distance away) with an uncontained fire after take off. The option would be there to do a quick radar circuit followed by a single channel, possibly single engined autoland. Think of the BOAC 707 that relanded on 05 at LHR in the late 60s (?) if the London area had been fogbound what would have been their fate?, I can only speak for the 737-200 but I would assume this would work on later models.