"Free feeding" refers to leaving food out for your dog all day, so that he can eat whenever the mood strikes him. I've seen this work for some people, so please don't interpret this post as nagging at those who practice free feeding. However, I do want to share my reasons for meal feeding as you they may help someone who is running into some issues.
"Meal feeding" means providing your dog with his food at specific times of day. Some prefer to split a meal up into two or more portions; I like to feed the entire meal in the evening. My dogs also get treats/snacks randomly during the day as part of routine and training. Here are some of my reasons for doing this:
1) Food Aggression/Guarding
A couple of my dogs came to me with food aggression and required a lot of work to correct it. Continually putting them in a situation where tensions around the food bowl may arise is just asking for trouble. Over time, those tensions could evolve back into actual food aggression and we would be back at square one. You may even find that after a while, a dog who previously didn't appear to have guarding issues will develop them as a result of the stress around the food dish.
I feed the dogs in their crates to keep meal time a mellow, unstressful, event. Every day the dogs go right into their respective crates to wait for their meals and at the same time, they practice patience. Every day they practice leaving each other's food alone as the crate doors remain open until after I have poured food into each bowl. There's no tension, because they know what is theirs and what isn't. They know they will get food if they wait and that their turn is coming. They don't focus on each other during that time, because they know that it makes more sense to focus on ME; the person who makes the entire situation happen. It doesn't feel like a training exercise, but that's exactly what it is. Best of all, this behavior carries over into treat and toy time too, where no crates are involved. The focus is on me, as the person who fully controls the act of dishing out food and other rewards in exchange for good behavior.
2) Picky Eating
Growing up, we had dogs that were picky about what they ate. We always free-fed our dogs and I feel that this was part of the problem. They got used to the boring food always being there so were always on the hunt for something better and more appetizing. While meal feeding won't guarantee that you won't have a picky dog, it can definitely help prevent that from happening with many.
3) Monitoring Intake
If you have multiple dogs like I do, leaving bowls of food out all day makes it difficult to figure out who is eating what. You could end up having trouble getting the right amount of food to each dog. I have a couple that tend to gain weight easily and a couple that tend to need a little more to keep their weight up. Feeding separately and at a set time helps me make sure everyone is getting the amount that they need. This is especially important if you have dogs on different types of food (such as puppy formula, large breed formula, or a senior formula).
4) House Training
This one is huge. If you know when your dog eats and how much, you'll be able to adjust feeding times to help prevent potty accidents. This is especially important with a new dog or puppy; a dog who eats late at night or while you're out of the house for a few hours is going to have a harder time waiting for the next potty break. Sometimes this simple detail makes all the difference in house training.
5) Crate Anxiety
Dogs who are anxious about being in the crate can be helped immensely by routine and by making the crate a positive, calming place. Nothing says "positive" or "routine" better than a meal delivered in the crate at particular times of the day. My latest foster failure came back to me with some crazy crate issues which we tackled over the course of a couple weeks with getting him back in the habit of having a routine and meals in his crate.
As I mentioned before, you might free feed and have no issues, and that's fine! But this information may prove particularly useful for those with multiple dogs or a dog that lives with small children (see item 1 about guarding). Those of you who foster dogs may already be very familiar with this routine, and if you're not, you may find a lot of stress relieved by implementing a meal feeding schedule as opposed to leaving food out at all times.