It can even become wrong for future dates. Always use UTC is a broken, bad rule for future dates, it only makes sense for things that have already happened.
As for how it breaks, you have a booking for 8pm the day after the start of summer time. You stored the date/time in UTC. Government changes the start of summer time. Your database now thinks it's at 7pm because it uses UTC.
As for how it breaks, you have a booking for 8pm the day after the start of summer time. You stored the date/time in UTC. Government changes the start of summer time. Your database now thinks it's at 7pm because it uses UTC.
Here's some examples:
https://codeofmatt.com/on-the-timing-of-time-zone-changes/
Also the EU is seriously debating getting rid of clock changes, and it comes up in the UK semi-regularly.
Your database will not fix your bad data when that happens.