Like every year the time in rich industrial countries is being adapted to "summer hours" in the begin of the spring and back to "winter hours" in the end of autumn.
Why is that needed? It's all about making more money. If you look at time as something not being determine by genius physicians but by commercial minded salesmen .. then you know that time is introduced to measure the labor/duration before there can be profit.
Playing with the measurement of time (switching summer/winter time) is to make sure that all the workers are spending the best hours of the day at work!
I've found a more "scientific" explanation at this wiki page: http://en.wikipedia.org/wiki/Daylight_saving_time (called the DST - Daylight Saving Time)