My understanding is that it is because it changes historically that you'd rather want +/- (an absolute measure) rather than Continent/Location denonimation (a measure that is bound to change).
If you want to record a local timestamp historically (e.g. log that this event of the electric facility happened at this time in the history of the facility, at the location of the facility), you want to say exactly when it happened, in the local time of the place, notwithstanding political/societal changes to the timezone it is attached to.
Does this make sense? Talking about time always makes things confusing.
Right, for explicitly recording a timestamp without having to refer to a historical time zone database it would seem to make a tiny bit of sense... but recording the actual time zone would work just as well for historical data and future times. I just have a hard time imagining a scenario where you really care about the offset... the timestamp itself is enough.
Maybe it's just historical baggage from not wanting to keep that historical record of time zones around for all eternity?
I dunno. It's a bit weird to me. It's a very indirect (precise) measure of something that doesn't seem like it would have much use over just recording the direct measure (TZ and/or just the UTC timestamp)
The more your learn about datetime the more confusing it gets, I suppose :). I guess it's good to know that it can get very confusing (and therefore to tread carefully) and to temper one's expectations of datetime libraries.
If you want to record a local timestamp historically (e.g. log that this event of the electric facility happened at this time in the history of the facility, at the location of the facility), you want to say exactly when it happened, in the local time of the place, notwithstanding political/societal changes to the timezone it is attached to.
Does this make sense? Talking about time always makes things confusing.