How does it have a negative impact if you have more usable hours in the evening ?

Summer evenings don't get comfortable until after the sun goes down, before that it's usually too hot to spend outside in the sun. We should move the clock an hour in the opposite direction, so the hot parts of the day are during working hours (when you're in a nice airconditioned office) and the cooler parts are in the evening, when you want to sit in the garden and have a beer and a BBQ.