It presumably also helps people who want the accessible or bicycle doors, if position of these varies (and they know which is where).
If done in conjunction with platform markings (platform vinyls/paint, zones signs etc) then it makes sense.
I think over the years, TOCs launching fancy new trains have talked a lot about their new classes of train, and of course given some of them names (GTR wanted to give 700s a name and even ran a competition, but I guess they never came up with anything good enough!) so the general public are becoming more aware of trains by numbers/names.
I think the next positive move would be to use the screens to show the headcode, along with route planners doing the same, so there can be no doubt over whether the train is the one you want (especially useful if there are trains leaving a terminus at the same time). People are used to flight numbers, so you don't need to be a trainspotter to benefit.