If you have the luxury of being able to sleep well regularly then an hour here or there can be accommodated for without terrible disruption. However, a lot of people work more than 40 hours a week, and have significant commute times as well. Typically what ends up suffering is sleep. When people are chronically sleep deprived shifting an hour earlier can have a huge impact (e.g. going from 6 hours of sleep to 5, or even 5 to 4).

Also, sleeping in on Sundays doesn't help. By definition if you don't use the new time to control when you wake up on Sunday morning then your sleep schedule will not be adapted to the new schedule at all. All that will be different is you will have a stronger incentive to go to bed an hour earlier due to the time on the clock, though your body will still be set to fall asleep and wake up an hour later.