[remus]

> Appointments are made in local time. Store them in local time.

You may just be illustrating a particular use case, but it is more ambiguous in the general case. For example if you have arranged a meeting with someone in another timezone then maintaing the local timezone could lead to a misalignment for one of the participants.

[ivan_gammel]

This is ok. When future local user time offset is unpredictable, pinning meeting time to a certain location is a good strategy. If at some point meeting shifts for some user, well-designed calendar app could warn them and let reschedule. It still works better than pure UTC because it is predictable for at least some of the users.