Free
ranging your chicken flock has a lot of advantages (and just sounds idyllic),
but you’ll also run into several problems.  If you understand the
potential pitfalls up front, chances are you can work around them and
give your flock limited or complete access to free range.

• Predators — Coops,
  pastures, and chicken tractors give your flock some protection from
  predators (not least because they keep the chickens under your watchful
  eye.)  The reality is that free range birds are a lot more prone
  to be eaten by hawks,
  foxes, raccoons, neighborhood dogs, and even your own pets (if you
  don’t train them well.)  You’ll have to decide whether losing an
  occasional chicken to predators is worth lower feed costs and healthy
  chickens.
• Garden damage — Don’t
  let anyone tell you that chickens and gardens mix, because they
  don’t.  Chickens are very good at eating your tomatoes, scratching
  up seedlings, and strewing mulch all over the garden paths.
  However, we have recently discovered a few ways to work around this
  problem and still let our chickens out from time to time.  One
  option is to fence off the garden — even a partial fence can do the
  trick.  We let our laying flock out on the back side of the
  pasture, and they just don’t feel like walking all the way around the
  pasture fence and barn to get the garden, so they’ve been foraging in
  the woods.  Another option is to let young chickens free range,
  then corral them once they reach two months old (at which point we’ve
  found they begin to scratch up the garden rather than just weeding out
  the chickweed.)  Finally, if you only grow vegetables in the
  summer, you can turn the flock into the garden area after the first
  killing frost and let them eat up weeds and insects, fertilizing the
  ground for next year.
• Coming home to roost —
  The
  more your chickens roam, the less likely they are to come home to the
  coop at night.  This is a problem for several reasons: more chance
  of getting eaten at night if they’re further from home; less chance of
  laying in the next box where you’ll find their eggs; and tougher to
  manage birds if you can’t pluck individuals off the roost at night to
  cull or separate.
  It’s important not to let your birds get into the habit of
  roosting in the trees (like our laying flock did last week when they
  got stuck in the bushes, not realizing they’d have to backtrack in the
  wrong direction to get home.)  Saving a bit of your chickens’
  ration to be fed at dusk is a great way to get them to come home.
• Chicken poop — Your
  chickens will probably like to hang out where you are, which means
  there will be blobs of chicken poop on your front porch, your walkway,
  and everywhere else.  If this bothers you, you might choose to
  fence off select areas.
• Unhappy neighbors — Our
  closest neighbor is half a mile away, and I’m 99% sure our chickens
  will never make it across the creek and through the woods to bother
  them.  However, closer neighbors might be less thrilled to have
  chickens scratching up their vegetable garden and pooping on their
  steps.  Good fences make good neighbors (and I’ve heard gifts of
  free range eggs help too.)

We’re resting our pastures this winter by free ranging the flock as much as possible, but we’re also taking our own advice.  Once the nine week old broilers started scratching up my garlic, they got relegated to the orchard half of the yard, and we’ve been giving them a snack every evening before shutting them in the coop for a safe night’s sleep.  So far, we’re enjoying the best of both worlds — happy and healthy chickens and a free range method we can live with.