[CodesInChaos]

That is usually enough when recording events that happened at a specific point in time. Even then you sometimes want to record the offset in the user's timezone, so you know the relevant local time (e.g. when taking a photo).

But it's not enough for things agreed to happen in a specific time zone (meetings, contracts, subscription billing, etc.) In those cases you have to record the local time and timezone name (plus disambiguation for DST switching) and figure out how to handle changes of the timezone definition (e.g. by updating denormalized UTC representations or offsets).