I also like to do scheduled feedings for trick training, in addition to potty training. This way you will know when they are on an empty stomach and most likely will do whatever you want them to to get some kibble!
Uni didn't know what a treat was until she was more than 2 yrs old. I think this really helped a lot with our trick training.
If I were to free feed, I would put out the alotted amount per day, and no more. They they will learn quickly if they eat it all too early, they will go hungry throughout the day.