Free feeding - don't. Plain and simple; just don't do it and here's why. First and foremost can you imagine having a big old pile of food on your counter all day, all night there for your every whim. It may be cool for a day or two but you would grow sick of looking at it and if you are like any normal human you would have eaten way too much of it. Now just looking at it makes you feel sick; so if this is your only food source you will probably pick at it, but the gusto is long gone. Dogs who are free fed are usually poor eaters.
Now, not all dogs grow sick of eating and those who still enjoy eating and have a bowl of food that is always full risk the chance of becoming obese. Fat dogs are fat through no fault of their own; nope it is the humans who create fat dogs. Just picture your dog while you are at work all day. They are probably bored; what do you do when you are bored? I often eat; yes it is a bad habit but dogs will do the same, again increasing their risk of gaining extra pounds.
Leaving food out all day and night is not healthy; food goes bad. And the better the quality the faster it goes bad. If your dog is not cleaning their bowl everyday and receiving new fresh food then how do you know that the kibbles on the bottom haven't been there for a really longtime? Eeeewwwww. When a dog is constantly nibbling it is very difficult to know when they are going to need to relieve themselves. For puppies this makes housetraining extremely difficult and making sure that your dog goes before you go off to work in the morning can be very difficult.
Free feeding has no benefit except that I guess it seems like the quickest and easiest way to do a job that must be done. Just keep filling the bowl that is sitting on the floor, day in and day out. There are other reasons not to leave a bowl of food on the floor as well. You have no control of food in your house. Being the controller of the food is a big deal and a good deal. It makes you, well the food holder and that position is one of power. Not that I'm power hungry but it can give you a chance to work on some issues.
There are times when I don't even feed out of a bowl at all. Even though my dogs typically eat something different at every meal, I often will chuck food around the yard, use it for obedience purposes or just plain behavior training. Having your dog sit and wait for their portion of food without fighting with the other dogs is a highly desirable behavior. Even if you only have one dog, could you sit nice and quiet while fork feeding your dog some steak? Most people would say NO. Manners is so very important and to miss out on the use of meal time to work on them you are really losing out.
Think about that bowl of dry corn chips on the counter, there for your nutrition for the rest of your life. Then consider spicing it up and take back feeding time as your own. You bought the food, control it.