Oh I agree for the starting station, eg: Euston or Kings X, it's the ability to reserve seats as the train progresses that concerns me.This is overtalking the issue somewhat. Trains are designed to be able to move around them safely while in motion.
It's an annoyance, that's all. But it does have benefits - for instance, being able to reserve seats right up to departure and separate from ticket purchase makes the "Kings Cross scrum" rather less of an issue than the "Euston scrum".
I think they should have a cut-off time after which reservations aren't possible.
We don't want to get so reliant on reservations we end up with a RENFE type situation where every seat is reserved, no ability to turn up and go.