From London
https://www.mylondon.news/news/transport/full-list-london-underground-stations-27584387Full list of London Underground stations where customers forget to tap in or out the most as TfL» charges £32 million in maximum fares
Officials automatically correct journeys 'based on commuters' previous journey patterns', but customers can ask for a refund if they think the alteration is incorrect
There is a certain attraction in a fare system where you can simply tap in and tap out ... but also this downside.
It's a very minor downside especially in the context of the convenience of not having to faff about with tickets and knowing that you will pay the minimum fare for the journey you're making, and even if you do forget to tap in/out (as I have once or twice) the refund system is very swift and efficient.
The sooner it's more widely adopted, the better - especially bearing in mind that the majority of ticket offices will be disappearing shortly.
Should be added to the scope of fare simplification.