The only time using UTC breaks down is when any sort of time change gets involved.
If I say I want a reminder at 9am six months from now and you store that as UTC, a day light savings change will mean I get my reminder an hour early or late depending on where in the world I am
So TL;DR: there might be unexpected time zone rule changes in the future. The solution presented in the article is to store both UTC and local time, so the application can easily adjust itself if such change happens.
The only time using UTC breaks down is when any sort of time change gets involved.
If I say I want a reminder at 9am six months from now and you store that as UTC, a day light savings change will mean I get my reminder an hour early or late depending on where in the world I am
But wouldn’t you calculate the time in the future in the right time zone and then store it back as UTC?
It depends on the application.
I don’t remember all the specifics but this is the blog post I refer to when this topic comes up
https://codeblog.jonskeet.uk/2019/03/27/storing-utc-is-not-a-silver-bullet/
So TL;DR: there might be unexpected time zone rule changes in the future. The solution presented in the article is to store both UTC and local time, so the application can easily adjust itself if such change happens.