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IMO, the biggest problem with timezones is that the people who initially created them were fairly short sighted.
That and there have been way too many changes to who lives in what timezone. The one that boggles my mind is that apparently there's a country in two timezones, not like, split down the middle or anything, but two active timezones across the entire country depending on which culture you're a part of, or something. It's wild.
I still don't know if there's any difference between GMT and UTC. I couldn't find one. They both have the same time, same offset (+0), and represent the same time zone area.
I use UTC because I'm in tech, and I can't stand time formats, so I exclusively use ISO 8601, with a 24 hour clock. Usually in my local time zone, via UTC. We have DST here which I'm not a fan of, but I have to abide by because everyone else does.
My biggest issues with time and timezones is that everyone uses different standards. It drives me nuts when software doesn't let me set the standard for how the time and date is displayed, and doesn't follow the system settings. It's more common in web apps, but it happens a lot. I put in a lot of effort to try to get everything displaying in a standard format then some crudely written website is just mm/dd/yy with 12h clock and no timezone info, and there's nothing you can do about it.
UTC exists as a historical compromise because the British felt that GMT was the bees knees and the French felt differently. The letter order is most definitely a compromise between French and English word order. You can call it Universal Time Coordinaire.
Historically, GMT became the international time reference point because the Greenwich observatory used to be the leader in the field of accurately measuring time. It probably helped that the British navy had been dominant earlier and lots of countries around the world and across time zones had been colonised by the British.
UTC is an international standard for measuring time, based on both satellite data about the position and orientation of the earth and atomic clocks, whereas GMT is a time zone. Nowadays, GMT is based on UTC not independent telescopic observation.
What's the difference? You can think of a time zone as an offset from UTC, in the same sense that a 24h clock time is an offset from midnight. GMT = UTC+0.
Technically, UTC isn't a valid time zone any more than "midnight" is a valid 24h clock time. UTC+0 is a time zone and UTC isn't in a similar sense that 00:00 is a time in 24hr clock and "midnight" isn't.
Of course, and perfectly naturally, I can use midnight and 00:00 interchangeably and everyone will understand, and I can use UTC and UTC+0 interchangeably and few people care, but GMT = UTC+0 feels like the +0 is doing nothing to most eyes.
Fun fact: satellite data is very accurate and can track the UTC meridian independently from the tectonic plate on which the Greenwich observatory stands. The UTC meridian will drift slowly across England as the plates shift. Also, the place in the stars that Greenwich was measuring was of by a bit, because they couldn't have accounted for the effect of the terrain on the gravitational field, so the UTC meridian was placed several tens of metres (over 200') away from the Greenwich prime meridian. I suspect that there was a lot more international politics than measurement in that decision, and also in making the technical distinction between UTC and GMT, but I'm British, so you should take that with a pinch of salt.
That's quite the lesson you just laid down.
It's actually made things a lot more clear for me. To put it as tersely as I can, UTC is the international time, GMT is a timezone, which also happens to be UTC+0.
So GMT is a place/zone/region of earth, and UTC is a time coordination, with no physical location (beyond the prime meridian, which is where it is tracking the time of).
Awesome.
I know people who actively fight me on ISO 8601. They don't like the way it sorts their files/folders, reliant on whatever behavior the operating system does. Whenever data recovery happens or their files are moved, all the change times are blown out the window and the sorting they expect is blown away.
I'm not yet using a 24-hour clock. But it has me thinking. That's not such a bad transition for 24-hour local time into UTC. Or just using both. At some point the inconvenience of the local will become vestigial and UTC is what remains.
I use 24h clocks and ISO 8601 dates almost always
Honestly, I'm better at organizing code than I am my actual life