It's handy if you're doing a genuine single journey (I've used one once for that reason), but if you price your walk-up singles at half the relevant returns that fixes it, too, without people ending up with Penalty Fares because they got on a different train on a high frequency urban route. Some of these APODs (e.g. on the Leeds suburban EMU services) are a bit like if the Metropolitan Line or Merseyrail had Advances, and I think we'd all agree that would be ludicrous. Whereas I can't really see an issue with them on medium distance expresses like Barrow or Windermere, where if one train is a 3-car and the one an hour later is 6, you might want to price as many people as possible onto the latter. Or for Manchester to Preston, you want to price people onto the 6-car Blackpools off the presently 3-car Barrow/Windermeres.