If you have backyard chickens and you wish to keep them in your backyard you might want to clip their flight feathers to prevent them from flying the coop. Sorry couldn’t resist. They can and do fly over garden walls and fences and this can land them in some dangerous situations.
While in your own yard, especially if you also have a rooster to protect the girls they are fairly safe but if the decide to fly out of the yard they then become free game for any dogs or even cats than may be around, not to mention they could get run over by cars or eaten by any number of predators. Clipping the flight feather will not hurt them and will need to be done at least once a year as they grow back.
Once they are clipped the chicken can’t get enough loft to fly over a fence. If you have free range chicken on say a farm or a large area of land clipping would not be recommended because when they are out in the open like that they need to be able to fly short distances to flee predators. Living Homegrown has a great tutorial on clipping the flight feathers so you can clip your birds wings and help keep them in the yard, I used to clip my parakeets wings this same way so they wouldn’t fly into windows and walls when I would let out of the cage. The could still flap their way onto the table or sofa but not launch themselves headfirst into walls or glass.