Except the problem is that the office worker still needs to know the offset for Sydney. Either way you're still memorizing offsets, it's simply a question of what you want to call them. As long as people around the world have schedules that are offset from each other, there will be a need to know what those offsets are. The time zone system is simply a method by which various areas can declare what the offset they want to work under is. It doesn't matter if the lines are clean on a map. I could have an island in the middle of the pacific, and declare it part of the GMT time zone, and as long as the businesses on that island are generally open from 9 to 5 on the time zone I've chosen (maybe a bunch of serious night owls?) then the system is working fine.