It's fairly unusual to have a system where people can write timestamps in arbitrary timezones. Most of the time there's a suitable context where a timezone just

It's fairly unusual to have a system where people can write timestamps in arbitrary timezones. Most of the time there's a suitable context where a timezone just makes sense For example, in a booking system the timezone will be associated with the venue or the destination. In a scheduler for a trading system certain timestamps (start, stop time etc) will be the timezone of the trading venue. For past events (logging) UTC essentially always makes sense.