Note that by no means I am an expert. This is information I have gathered by observation and reading. I mean free ranging as in without perimeter fences or anything, so you understand what I mean.
I free range my chickens. My dream farm is on at least twenty acres, with huge multiple acre pens for each breed, and their own pens too of course. But we have an acre, and that kind of farm can be expensive, so we have one acre and choose to free range them. Doing this takes a certain kind of flexibility, it may not always work out.
These are some problems that come along.
Locking them up at night
When we lock them in for breeding, they may get agitated.
In the winter, we keep them inside due to subzero temperatures
Predators. We have only lost one bird to them, since we live in an area where predators are scarce. That is the reason we run the risk of free ranging. If you have daytime predators, don't free range.
Only for the breeds that can handle it. Bantams are easier predator targets.
Neighbors, we have none within an eighth mile. If you have some next door, and you live in the city, don't do it.
Why I like it:
Gives them a variety of food.
Cheaper, no artificial light, we also need less windows.
With us living on an acre with fields around and an enormous shed in the middle, and a mound and an old concrete cow yard it would be difficult to separate it into breeding pens for different breeds. We just have a chicken tractor and some cages that we separate the chickens out in to a different times of the year.
Cost. It costs less to free range. The cost of feeding, fencing, and lightning/windows is less.
Honestly, I would only recommend free ranging to those with few predators, no next door neighbors, little land, are willing to lock them up at night, catch them, and if you live in a temperate climate, not during winter. Our chickens enjoy it, but you also have to pick the right breeds. All large fowl, except white Cornish cross fare fine. Some delicate bantams have trouble, and free ranging with its dampness, can cause feather footed chickens to wreck their feathered feet. It's just one of those things that works well for me that I wouldn't recommend to others.
And remember to give them well ventilated, well insulated housing to retire to!
So, if you are willing, go for it!