Originally, DST was to provide similar waking hours year round and provide the most light hours during those waking hours. Why conserve light? Especially pre electricity, being awake in the dark was counterproductive. Now it is energy usage, but it used to be dangerous to use lights since all were fuel based, and many fires resulted. People tend to sleep until they need to rise for work or whatever, so work should theoretically begin just long enough after dawn to allow people time to prepare. This works great for a short period, but dawn shifts by more than an hour over the course of a year. (bigger changes as you move toward the poles.) This left the option of changing work hours during the course of a year or changing the time with respect to dawn.
The biggest reasons nowadays are to conserve electricity and for safety. Someone here mentioned to have the time changed so it would get light at 8AM. Their point is that going to work in the dark is no big deal and leaves more light after work. Unfortunately, school is timed to start at or before start of work so parents can take their kids to school en route to work. For parents whose children ride the bus, this is a serious safety issue since they don't want their kids walking to the bus stop and waiting in darkness. This creates an increased danger of being hit by a worker who should still be in bed and still aren't alert as they pull out of their driveway, and an increased risk of abduction since the darkness provides a degree of protection from observation for criminals.
So while it does have drawbacks (the "spring forward" Sunday REALLY sucks!) I will stick with supporting DST.
