I went to a seminar a few years ago and one of the topics was Putting. They did a statistical breakdown which I thought was very enlightening.
To summarize it they suggested that people should practice two lengths of putts. Long putts, 25 to 30 feet and short putts 3 to 5 feet.
Based on their data of approach shots into the green, most peoples first putts are not in the 10 to 20 foot range.
So with the understanding that most people do not practice putting much, this can help to narrow their scope before a round or if they do get a chance to practice it can maximize their time.