> If you are writing calendar software, it is legitimate to have "floating time" i.e. your medication reminder is at 7pm every day, regardless of time zone, travel, or anything else.

If you have to take medication (for instance, an antibiotic) every 24 hours, it must be taken at the same UTC hour, even if you took a train to a town in another timezone. Keeping the same local time even when the timezone changes would be wrong for that use case.