That depends on the size of your flock and the size of your yard. Big flock~small yard= eventual smells, especially in the summer time.
If your yard is reasonably big and your flock small or average, you shouldn't have any smells to contend with. Their droppings won't kill the grass unless the above conditions are present, then their mere presence of trampling, scratching and pooping will kill off vegetation.
I have an acre on which mine free range and I have two dogs who guard them.....the dogs clean up the chicken poop and the chickens clean up or disperse the dog poop, so I don't usually have any kind of odor or feces problems with my setup.