The setting changes HOW time is shown and changes nothing in the data itself: measurements and events are stored unchanged.
The zone also decides which day counts as today when you enter dates. That matters more than it seems: before this setting the day was taken by UTC, and on a farm in Thailand today's date could not be picked at all before seven in the morning - the calendar treated it as the future.
Pick a zone, not an offset in hours. Where daylight saving time exists, the offset changes twice a year, and a record made in spring would read wrongly in autumn. The current offset is shown next to the zone name, for example Asia/Bangkok (UTC+7).
The zone is shared by all farm members. This is deliberate: otherwise two people discussing the same measurement would name different times.