Apart from the road closure issue, An earlier start means you have the rest of the day free to spend time recovering / in the pub / with family.
Our local 10k race starts at 1pm on a Sunday and that really is a pain in the neck - it means hanging around all morning in the house or in the garden waiting for the time to near. Also by the time you finish, cool down, etc it's nearly 3pm, and too late for lunch, but a bit early to go home for the rest of the day.