The importance of running on different surfaces.

Running on roads,

While the roads are always readily available for running, they’re not the best for your body. 

If its possible, find a softer surface to run on at least once a week, be it a familiar path in the woods, grass field on your school grounds or path through the park.

Not only will you keep those everyday aches and pains to a minimum, but you’ll recover quicker, strengthen your ankles and develop your lower leg muscles more rapidly. If you have had a previous injury, and you are coming back into exercise, running on grass or soft track surfaces, this will strengthen your muscle around your knee, giving it an easier chance of healing. If you were to run on the roads after an injury, the impact of your knee when hitting the road, would but pressure on the knee, and sending pain around the whole knee.     

If you thought the grass, or some other similarly soft surface, you guessed right. Not only will you keep those everyday aches and pains to a minimum, but you’ll have a much better chance of a quicker recovery, strengthen your ankles and develop your lower leg muscles more rapidly.

Grass
Pros: Grass is soft and low impact, so it may be a better choice for people who have bad knee injury's. It's usually rated as one of the best running surfaces.
Cons: A run in the park can be a little stressful! Besides hidden holes, rocks, and twigs, you also have to watch out for other obstacles, like pedestrians, dogs, and other distractions.

Concrete
Pros: Running on the footpath can be the most convenient if you live in a city, and it also may be the safest option if you don't want to risk it on the road.
Cons: Concrete sidewalks are one of the hardest surfaces you can run on, which may lead to more stress on your joints and muscles. Most running experts recommend you try to limit your time on the footpath..And if you have injuries like ankle sprains or knee pain, it's probably best if you stay off the road.

http://www.popsugar.com/fitness/What-Best-Type-Surface-Running-18439612

http://running.competitor.com/2014/06/training/the-importance-of-varying-your-running-surfaces_5889