For myself, I've always been a "morning" person. And I've noticed that during hard training cycles any tough workouts after about 5pm or so end up keeping me "revved" up for hours. It interferes with a good night's sleep. Far better for me, for getting the day started right (blood flowing, muscles stretched and energized), is a morning workout. Hasn't always been possible, but for me it's far preferable. If only to keep me up and at my best during the best part of the day, and to allow me to sleep better without the body still wanting to go, go, go.
Everyone is different, though. Not everybody's daily rhythms are so ingrained.