Why MySQL’s DATETIME can and should be avoided

Right, stop using those "complicated" built-in date processing functions and instead roll your own. What could possibly go wrong? Storing a number that's only meaningful when defining it somewhere outside of the database is much more fun! Finally you get to meet all your co-workers in person, at least all the junior developers who will stop by your desk to ask why there are these weird numbers in the date columns.

tldr: In this article from 2009, consider storing UTC plus the local timezone instead of the local server time when building applications that have users in multiple timezones. Use a time or a time offset as appropriate to capture a point in time (e.g. a birthday) or a timespan (e.g. the number of seconds this thing ran), resp.