[Denvercoder9]

Converting from a local date/time with an associated timezone to an UTC time is not a lossless nor unchanging operation. By converting everything to UTC, you're throwing away information that you might need to do the conversion at the 'last mile' later on.

For example, imagine I schedule a dentist appointment for 9AM in my local timezone sometime next summer, and put it in my calendar. Now, if the government decides that we won't do daylight saving times next year, my dentist and I still expect that appointment to happen at 9AM local time. However, if my calendar application had converted it to UTC using the timezone definitions at the moment I created the appointment, it would show in my calendar at 8AM, and I'd be an hour early!

This is not an as hypothetical situation as it seems. To give just two recent examples: the Chilean government decided to postpone the start of DST with less than a month's notice last year, and Morocco shifts the clock an hour during Ramadan, the date of which only becomes certain on the day itself.