I have worked as a producer, and I've also worked on sets for A.D.s as talent. My personal feeling is you get better results by being a morale raiser than a ball buster.
Therefore, when you get the opportunity, call a quick meeting and tell everyone what a great job they're doing and how pleased you are to have such a great crew. Then tell them, one of the best ways to get more work is by creating strong relationships and the best way to do that is by making a good impression on people who can hire you again and refer you to other jobs.
Let them know that by talking in between shots, it could give the impression to the "higher-ups" that they're not focused, not taking the job seriously, or are just unprofessional. Suggest that they stay focused during the hours of the shoot and then, hang out and have fun with each other after the day is wrapped.
For more tips and articles by top entertainment industry career coach, The Greenlight Coach, visit www.TheGreenlightCoachBlog.com