When I work with training people and their dogs, I find that it is sometimes a challenge to get people to say just the command. If I ask people to tell their dog to "Sit," some people might say, "Please Sit," others might say the dog's name and the command, "Rover, Sit," and still others keep repeating the command like travelers in a foreign land dealing with people who don't speak their language.
While learning theory suggests that saying the command once and not saying anything else is the most effective way to train a dog, there has really been very little practical evidence to substantiate this.
A recent study provides a field and an experimental test of how well dogs respond to commands if their name or something else precedes the command (Braem and Mills. 2010. Factors affecting response of dogs to obedience instruction: A field and experimental study. Applied Animal Behaviour Science 125 (2010): 47-55).
In the field study, the authors videotaped 56 dog handlers giving their dog a "Sit" command. There was a roughly equal mix of male and female dogs that were used, of a variety of breeds, and the handlers ranged in age from 10 to 60-plus. The authors found that two factors influenced the dogs' performance in obeying the command: the attention that the dog gave to the handler while the handler was giving the command, and the amount of verbal information that the handler spoke before giving the command. Both of these factors decreased the performance of the "Sit" command.
In the experimental study, the authors used 12 dogs of various breeds, with only one handler who was always dressed the same and acted the same when giving the commands. The handler taught to the dogs to respond reliably to a known command (e.g., "Down"), and to a novel command ("uff" to signal jumping up on a platform where there was a reward).
Then the authors did a series of experiments where each dog was given one of several combinations of commands: the dog's name, followed by a one-second pause, then either the known command or the new command; and an unknown word (the German "Banane") preceding either the known or the new command.
The authors found that saying the unknown word before either the known or the new command significantly decreased the dogs' performance. Saying the dog's name prior to the known command ("Down") had no effect on performance, but saying the dog's name prior to the new command ("uff") decreased the dogs' performance, just like saying the unknown word before a command.
So the results of this study substantiate the predictions of learning theory. Saying just the command is better than saying anything else along with it, although saying the dog's name does not seem to have any effect, as long as the dog is very familiar with the command.
Saying "Rover, won't you be a good dog and sit down, pretty please?" just doesn't cut it in training dogs to respond to a command.