Why would you want to train your small dog to eat only from you? You teach your children not to take candy from strangers, why not your dog?
There are several good reasons to teach your dog only to eat from you. Small dogs can have sensitive stomachs, especially if they are only used to getting one type of dog food, or if they have allergies or other health conditions. A well-meaning outsider may think they are doing your little dog a favor by giving him the end of their hot dog or sharing their meal, but this could upset your small dog's stomach--and they won't be around when your dog gets sick all over your bedroom carpet!
Other health-endangering incidents can occur when your dog finds food out on walks. Food left out and about in the environment may be poisonous for your dog, such as candies containing artificial sweeteners, or foods that may be rotten or have been intentionally tampered with to harm dogs. Some neighborhoods have a problem with individuals poisoning dogs indiscriminately or by directly targeting dogs. Teaching your dog to only take food from you will prevent him getting sick from eating food accidentally that would upset his stomach or harm him by intentional poisoning; there are bad people out there!
Teaching your dog to 'leave it', which can be directed at your dog in a specific situation can be useful but requires you to be present to give the command. Teaching your dog to avoid taking any food not offered to him by you\ can protect your small dog when you are not available to supervise, but can present difficulties if you are away or you or your dog is ill and your dog requires care by others. Teaching your dog to eat from a specific bowl or type of bowl may help control his eating behavior and provides some flexibility. Be sure to pick the right behavior for your situation.