Which is of course an over-simplification that happens to work just fine for your purposes. But while freight headcodes do tend to be unique, especially useful when tracking down all those one-off workings, on the passenger network that is definitely not the case. Not only can numbers repeat over time on the same route in a day they can also be duplicated in different parts of the country. As such they are of little use to ordinary passengers though many enthusiasts continue insisting on referring to them.
It has long been the case that probably the keenest users of headcodes are members of rail staff who happen to also be rail enthusiasts. In some cases using headcodes rather than referring to times and origins/destinations is a way of talking in a code understood only by those in the know, almost as a form of snobbery. And of course there are also non-staff enthusiasts who enjoy the feeling of being on the inside by joining in this way of communicating. Never could see the point of it myself given that headcodes don't appear in public timetables unlike their equivalents in Europe but each to their own I suppose.
.... It's Horses-for-Courses (says he who has just spent the weekend photographing friends show jumping - How "snobbish" is that
) in that if you are travelling by rail and want information, then an app such as RTT can be a real aid either with or without a headcode.
But if you are a ferroequinologist (as I am), then you are
primarily and most likely
only interested in the spots on a train's journey where you can go to see or photograph them. In which case, a headcode irrespective of its source is extremely useful and its information can save a lot of time and also cost in fuel - It's a very efficient shorthand and RTT plus Traksy are the apps I find most helpful alongside each other. Most railway enthusiasts are more interested in freight trains, charter trains, engineering and test trains, light engine movements and locos rather than mundane everyday passenger trains, although a panned motion-blur pic of a 'Cucumber' (Class 800 series) can look quite good.
Whether a headcode is given by a fellow railway enthusiast or a railway employee or an app, its source is entirely immaterial - It's simply a shorthand which saves everybody from wasting time writing an essay.
Indeed it is "each to their own" but without the reluctant spin of "I suppose".
BTW, it's fun to switch into being 'snobbish' when certain circumstances prompt it.
things i learnt today: you can search headcodes on RTT!
.... Sometimes RTT's Simple Search doesn't give any headcode but their Detailed Search is usually more reliable. I hope this helps
.