I live in the suburbs on a large lot and my Australorps free range every day from sunup to sundown.
We built an 8' fence to keep the deer and dogs out and the chickens in. Although the chickens weren't flying over the 4' fence that was there before we built the new one, stray dogs would have easily cleared the fence. Dogs are likely to be out and about at all hours of the day and night. As far as predators go, dogs are the ones who have the most potential to successfully attack my flock.
We live in a heavily wooded area that abuts some small forest tracts and we've seen both raccoons and foxes in our yard. That being said, both of these predators are typically nocturnal hunters. That doesn't mean that they'd never come to my yard for a mid-day snack, but it's not something that I'm overly concerned about. It's possible that they could attack my hens, but not probable. Aerial predators are also a consideration. I frequently see birds of prey flying above my house, and I see how the chickens react. When they see a dark silhouette overhead they freeze and make a very distinctive trilling sound. Even though I've seen these predators, I don't worry about them because our lot is so heavily wooded, the chickens have lots of places to hide and landing and takeoff would be difficult for one of these birds of prey. Someday I may be eating crow for saying that chicken hawks aren't likely to go after my birds, but for now, I just don't see the danger as imminent.
The advantages to free ranging are numerous. No more Frontline for my cats because there are no fleas or ticks left in our yard.
Also no more snakes. My coop and run are empty during the day except when a hen goes in to lay an egg, so there's less poop build up than there would be if the birds were cooped up during the day. What this means for me is that I don't have to clean out the coop. I stir the shavings and that's it. The nighttime poop dries out and that's that. No smell at all. I use DE with my shavings and don't have a fly problem in the coop. Maybe the DE plays a role in this. Maybe I've got naturally occurring fly predators in my "not cleaned out" coop. Who knows. All I know is I haven't got flies in the coop.
In addition to providing protection from aerial predators, the trees cast lots of shade. It gets pretty darn hot here in NC, but my birds can always seek out the coolest spot. The coop is shaded almost all day, but it's still always somewhat warmer than the ambient temperature.
My chickens also don't seem to eat much feed. They spend all day scratching around for beetles, worms, other creepy-crawlies, and sprouts. I say sprouts because the weeds don't really have a chance to grow into little plants. The chickens find them before they break the surface of the earth and eat them.
I do have an enclosed and completely predator proof run attached to my coop, but the girls really don't enjoy being locked up in it, and they let me know it. Me and all the neighbors, too. Mine make much more noise when they're locked up. Perhaps this would be different if they'd never been able to roam freely. I'll never know because I'll never raise chickens that can't roam freely. I wouldn't enjoy having them if they were relegated to just 120 sq.ft. rather than the whole back yard.
You know, there are pluses and minuses to everything. Sure, a desperate fox could show up during the day and kill one or more of my chickens. But if I kept them in a smaller enclosure, I could have issues with feather picking and bullying like so many other people who post on this forum. I might see more disease in my flock if they were kept in close quarters. And I'd surely have lots more work trying to manage the litter and run. Maybe it sounds heartless, but I'm willing to take the small risk that a predator might get my chickens if it means that I can let them do what chickens do.
I've spent lots of time reading through the predator threads and it's heartbreaking, I'm sure, when you come home to a massacre. But, having watched my chickens roaming the yard day in and day out, I'd be heartbroken if I had to keep them penned in a run. Everyone's risk tolerance is different, as is everyone's backyard setup. This is what works for me (and what wouldn't.) I hope my two cents helps.
Good luck.