>... if I wrote that my time is 14:09 CEST then, if you care, you would also know that I’m writing from Central Europe and not from Egypt, from Central Africa, from South Africa, or from the Kaliningrad Oblast in Russia.
Yes, but this doesn't hold up across the entire database. Consider CST might mean Central Standard Time, China Standard Time, Cuba Standard Time, etc. BST might mean British Summer Time, Bangladesh Standard Time, etc...
It only really works when the user has some other context, such as foreknowledge of country.