Absolutely. You wouldn’t believe the troubles I’ve had by burying a single digit of hard-coding in the midst of a ton of stuff that depends on that one magic number. Can I change it? Dozens of ways. Will I remember, though?
And delightfully enough, a PHPBuilder article on supporting user timezones that aren’t the server’s timezone starts out
By allowing the user to specify a timezone, we unwittingly opened a Pandora’s Box, out of which flew shrieking timestamp demons who tormented us, and drove us to the brink of insanity.
and ends up, speaking of supporting daylight/standard conversions
but for simplicity, we opted to leave that as an exercise for the reader
(hoping, no doubt, that the reader doesn’t know that the first user of any timezone-supporting application lives in Arizona, and doesn’t have daylight time, and the second lives wherever it is that they have a half-hour of daylight time. The third lives in Israel, where the starting and ending dates are set each year based on what works best with the movable religious holidays.)