Let's agree that "common sense" tells you that you should get to the platform 4 minutes before advertised departure time and it's not necessary to be there any earlier than that
This is taking into account that the doors might be closed 1 minute early.
Therefore, we are agreeing that arriving 3 minutes before door closing time is ok.
Therefore we are agreeing that arriving 3:45 minutes before door closing time is earlier than necessary.
If you turn up 4 minutes before the advertised departure time, and it turns out that the doors are closed 15 seconds before departure, your "common sense" rule means that you're there earlier than we've agreed is necessary.
Therefore, your "common sense" rule by definition means that people have to turn up earlier than necessary for many trains.
Which is why advertising the doors-closed time is more logical, would waste less of people's time, and would have no deleterious effect on train punctuality. So why not adopt that system?
You assume that people don't want to turn up any earlier than is necessary. I don't think that is correct.
From what I see every day most people are not comfortable with that, particularly if they are on a time sensitive journey, where there could be major consequences of missing the train. Very few people arrive at my local station within five minutes of the train being due.
Then you have to think of those with luggage who want to get to a particular place on the platform. They don't see arriving early as a waste of time. In contrast it is a positive, they get peace of mind and are in the right place to board the train with a more comfortable experience.
I doubt it would, and you'll always get someone who thinks they have a god given right to board before the train has departed just like the people who have missed their check-in time at the airport
Agreed. I don't think altering departure times would have any positive benefit at all.